I just closed and restarted Thunderbird a few times and got the following crash report message...

Accessibility: Active AccessibilityInProcClient: 0x400 AdapterDeviceID: 0x3e98 AdapterDriverVersion: 27.20.100.9664 AdapterSubsysID: 09341028 AdapterVendorID: 0x8086 Add-ons: mailmerge%40example.net:8.1.0,tbsortfolders%40xulforum.org:2.1.0,%7B786abda0-fd14-d247-bf69-38b2fc18491b%7D:3.0.0,%7B8845E3B3-E8FB-40E2-95E9-EC40294818C4%7D:4.1,previous-colors%40alkatrazstudio.net:1.2,EditMailSubject%40jcp.convenant:5.1,simplemailredirection%40ggbs.de:1.18,shrunked%40darktrojan.net:5.0.2,%7Ba300a000-5e21-4ee0-a115-9ec8f4eaa92b%7D:0.5.2b4,en-AU%40dictionaries.addons.mozilla.org:2.2.1webext,google%40search.mozilla.org:1.0,amazon%40search.mozilla.org:1.1,bing%40search.mozilla.org:1.0,ddg%40search.mozilla.org:1.0,wikipedia%40search.mozilla.org:1.0,default-theme%40mozilla.org:1.2 AvailablePageFile: 9634582528 AvailablePhysicalMemory: 7296970752 AvailableVirtualMemory: 138530464747520 BlockedDllList: BreakpadReserveAddress: 2419609370624 BreakpadReserveSize: 83886080 BuildID: 20210924213438 CPUMicrocodeVersion: 0xea ContentSandboxCapable: 1 ContentSandboxLevel: 1 ContentSandboxWin32kState: Win32k Lockdown disabled -- Preference not set CrashTime: 1632963527 DOMIPCEnabled: 1 FramePoisonBase: 9223372036600889344 FramePoisonSize: 65536 GPUProcessLaunchCount: 1 GPUProcessStatus: Running InstallTime: 1632905244 LauncherProcessState: 0 ModuleSignatureInfo: {"Microsoft Corporation":["msvcp140.dll","VCRUNTIME140.dll"],"Microsoft Windows":["midimap.dll","msacm32.drv","wdmaud.drv","msacm32.dll","mlang.dll","TaskFlowDataEngine.dll","ntshrui.dll","explorerframe.dll","twinapi.dll","pcacli.dll","wscapi.dll","cdp.dll","NetworkExplorer.dll","dataexchange.dll","NapiNSP.dll","pnrpnsp.dll","winrnr.dll","ondemandconnroutehelper.dll","usp10.dll","linkinfo.dll","comctl32.dll","msi.dll","shfolder.dll","dbgcore.dll","cscapi.dll","sfc_os.dll","wsock32.dll","oleacc.dll","msimg32.dll","wininet.dll","winmmbase.dll","webauthn.dll","secur32.dll","mpr.dll","directmanipulation.dll","winmm.dll","Windows.Globalization.dll","DWrite.dll","FWPUCLNT.DLL","rasadhlp.dll","urlmon.dll","srvcli.dll","iertutil.dll","BCP47mrm.dll","winhttp.dll","InputHost.dll","textinputframework.dll","Windows.UI.dll","OneCoreUAPCommonProxyStub.dll","Bcp47Langs.dll","WindowManagementAPI.dll","twinapi.appcore.dll","npmproxy.dll","dhcpcsvc6.DLL","version.dll","edputil.dll","dhcpcsvc.dll","MMDevAPI.dll","winnsi.dll","AudioSes.dll","avrt.dll","wtsapi32.dll","ksuser.dll","dsreg.dll","ColorAdapterClient.dll","mscms.dll","netprofm.dll","wshbth.dll","policymanager.dll","propsys.dll","nlaapi.dll","WinTypes.dll","d3d11.dll","dcomp.dll","CoreUIComponents.dll","CoreMessaging.dll","apphelp.dll","uxtheme.dll","dwmapi.dll","dbghelp.dll","windows.storage.dll","kernel.appcore.dll","dxgi.dll","winsta.dll","ntmarta.dll","rsaenh.dll","msvcp110_win.dll","umpdc.dll","IPHLPAPI.DLL","dnsapi.dll","netutils.dll","powrprof.dll","mswsock.dll","cryptsp.dll","CRYPTBASE.DLL","wldp.dll","msasn1.dll","devobj.dll","userenv.dll","sspicli.dll","profapi.dll","cfgmgr32.dll","win32u.dll","wintrust.dll","msvcp_win.dll","bcryptPrimitives.dll","KERNELBASE.dll","gdi32full.dll","ucrtbase.dll","bcrypt.dll","crypt32.dll","advapi32.dll","nsi.dll","setupapi.dll","msctf.dll","clbcatq.dll","gdi32.dll","combase.dll","ws2_32.dll","sechost.dll","psapi.dll","ole32.dll","shlwapi.dll","SHCore.dll","imm32.dll","user32.dll","kernel32.dll","shell32.dll","imagehlp.dll","rpcrt4.dll","oleaut32.dll","coml2.dll","msvcrt.dll","ntdll.dll"],"Mozilla Corporation":["thunderbird.exe","xul.dll","rnp.dll","nss3.dll","nssckbi.dll","freebl3.dll","softokn3.dll","ldap60.dll","mozglue.dll","lgpllibs.dll","prldap60.dll","AccessibleHandler.dll","ia2marshal.dll"],"Nuance Communications, Inc.":["dd10axa_x64.dll","nlutmgrhook_x64.dll","dgniedct_x64.dll","textservice_x64.dll","dd10hook_x64.dll","dragonlog_x64.dll"]} Notes: Has dual GPUs. GPU #2: AdapterVendorID2: 0x10de, AdapterDeviceID2: 0x1c8d, AdapterSubsysID2: 09341028, AdapterDriverVersion2: 27.21.14.6679FP(D00-L1000-W00001000-T000) DWrite? DWrite+ WR? WR+ OMTP? OMTP- ProductID: {3550f703-e582-4d05-9a08-453d09bdfdc6} ProductName: Thunderbird ReleaseChannel: release SafeMode: 0 SecondsSinceLastCrash: 55985 ShutdownProgress: profile-before-change StartupCrash: 0 StartupTime: 1632961839 SystemMemoryUsePercentage: 56 TelemetryEnvironment: {"build":{"applicationId":"{3550f703-e582-4d05-9a08-453d09bdfdc6}","applicationName":"Thunderbird","architecture":"x86-64","buildId":"20210924213438","version":"91.1.2","vendor":null,"displayVersion":"91.1.2","platformVersion":"91.1.0","xpcomAbi":"x86_64-msvc","updaterAvailable":true},"partner":{"distributionId":null,"distributionVersion":null,"partnerId":null,"distributor":null,"distributorChannel":null,"partnerNames":[]},"system":{"memoryMB":16182,"virtualMaxMB":134217728,"cpu":{"extensions":["hasMMX","hasSSE","hasSSE2","hasSSE3","hasSSSE3","hasSSE4_1","hasSSE4_2","hasAVX","hasAVX2","hasAES"]},"os":{"name":"Windows_NT","version":"10.0","locale":"en-US","servicePackMajor":0,"servicePackMinor":0,"windowsBuildNumber":19043,"windowsUBR":1237},"hdd":{"profile":{"model":null,"revision":null,"type":null},"binary":{"model":null,"revision":null,"type":null},"system":{"model":null,"revision":null,"type":null}},"gfx":{"D2DEnabled":false,"DWriteEnabled":true,"ContentBackend":"Skia","Headless":false,"EmbeddedInFirefoxReality":false,"adapters":[{"description":"Intel(R) UHD Graphics 630","vendorID":"0x8086","deviceID":"0x3e98","subsysID":"09341028","RAM":0,"driver":"igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32","driverVendor":null,"driverVersion":"27.20.100.9664","driverDate":"6-1-2021","GPUActive":true},{"description":"NVIDIA GeForce GTX 1050","vendorID":"0x10de","deviceID":"0x1c8d","subsysID":"09341028","RAM":4096,"driver":"C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumdx.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumdx.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumdx.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumdx.dll C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumd.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumd.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumd.dll,C:\\WINDOWS\\System32\\DriverStore\\FileRepository\\nvdd.inf_amd64_2fe2cee3562a012e\\nvldumd.dll","driverVendor":null,"driverVersion":"27.21.14.6679","driverDate":"6-9-2021","GPUActive":false}],"monitors":[{"screenWidth":3840,"screenHeight":2160,"refreshRate":60,"pseudoDisplay":false}],"features":{"compositor":"none","hwCompositing":{"status":"available"},"gpuProcess":{"status":"available"},"wrQualified":{"status":"available"},"webrender":{"status":"available"},"wrCompositor":{"status":"available"},"wrSoftware":{"status":"available"},"openglCompositing":{"status":"unused"},"omtp":{"status":"disabled:FEATURE_FAILURE_DISABLED"},"d3d11":{"status":"available","version":0,"warp":false,"textureSharing":false,"blocklisted":false},"d2d":{"status":"available","version":"1.1"}}},"appleModelId":null,"sec":{"antivirus":["Microsoft Defender Antivirus"],"antispyware":null,"firewall":["Windows Firewall"]}},"settings":{"blocklistEnabled":true,"e10sEnabled":true,"e10sMultiProcesses":8,"fissionEnabled":false,"telemetryEnabled":false,"locale":"en-US","intl":{},"update":{"channel":"release","enabled":true},"userPrefs":{"app.update.service.enabled":false,"browser.cache.disk.capacity":1048576,"browser.search.region":"AU","extensions.strictCompatibility":false,"widget.content.allow-gtk-dark-theme":false,"widget.content.gtk-high-contrast.enabled":true},"sandbox":{"effectiveContentProcessLevel":1,"contentWin32kLockdownState":4},"launcherProcessState":0,"addonCompatibilityCheckEnabled":true,"isDefaultBrowser":null},"profile":{}} ThreadIdNameMapping: 4760:"IPC I/O Parent",1688:"Link Monitor #1",6044:"Permission",14240:"Timer",19224:"JS Watchdog",14664:"TaskController Thread #1",3972:"TaskController Thread #5",10748:"TaskController Thread #0",14296:"TaskController Thread #4",17596:"TaskController Thread #3",7396:"TaskController Thread #2",18216:"TaskController Thread #7",18500:"TaskController Thread #6",7380:"Cache2 I/O",19256:"Cookie",19004:"Worker Launcher",18696:"VsyncIOThread",4056:"IPC Launch",12864:"WindowsVsyncThread",4576:"Compositor",17628:"ImageIO",2936:"IPDL Background",4468:"QuotaManager IO",10392:"HTML5 Parser",6096:"StyleThread#2",17632:"StyleThread#1",6264:"StyleThread#0",18728:"StyleThread#3",18788:"StyleThread#4",3768:"StyleThread#5",17044:"ImageBridgeChld",14560:"GMPThread",14884:"ProxyResolution",10592:"TRR Background",12756:"localStorage DB",2628:"PlayEventSound",19096:"DNS Resolver #3",18188:"DOM Worker",15124:"StreamTrans #55",12872:"StreamTrans #58",16620:"StreamTrans #64",6292:"StreamTrans #65",1612:"DNS Resolver #8",15840:"DNS Resolver #9",1244:"BackgroundThreadPool #7",12948:"mozStorage #10",1296:"DNS Resolver #10",2052:"DNS Resolver #11",12792:"DNS Resolver #12",17948:"DNS Resolver #13",18132:"StreamTrans #68", Throttleable: 1 TotalPageFile: 23678566400 TotalPhysicalMemory: 16967680000 TotalVirtualMemory: 140737488224256 URL: UptimeTS: 16886.76412 Version: 91.1.2 Winsock_LSP: MSAFD Tcpip [TCP/IP] : 2 : 2 : 1 : 6 : 0x20066 : 0x8 : %SystemRoot%\system32\mswsock.dll :  : e70f1aa0-ab8b-11cf-8ca3-00805f48a192

MSAFD Tcpip [UDP/IP] : 2 : 2 : 2 : 17 : 0x20609 : 0x8 : %SystemRoot%\system32\mswsock.dll :  : e70f1aa0-ab8b-11cf-8ca3-00805f48a192 
MSAFD Tcpip [RAW/IP] : 2 : 2 : 3 : 0 : 0x20609 : 0xc : %SystemRoot%\system32\mswsock.dll :  : e70f1aa0-ab8b-11cf-8ca3

the crash Id as described here would be much more useful. https://support.mozilla.org/en-US/kb/mozilla-crash-reporter-tb#w_viewing-crash-reports

But the send button will never be active unless there is a valid from and to: address, so your initial issue appears to be not what you think it is.

What happens if you restart Thunderbird from the help menu in troubleshooting mode and continue when prompted?

addresses are valid

restarted Thunderbird from help menu in troubleshooting mode and it did not help the problem.

So far, none of the solutions work. Send is still grayed. Not able to get any business or personal emails sent out. Please fix this.

I eventually got it to work after many days. I needed to basically remove Thunderbird remove every relationship to Thunderbird of the computer and then remove everything in the registry. After this was done the program was reinstalled and then link to the old profile location. Now it works.

Something is getting corrupted during the update process. I will see if I can find a link for you to the webpage which shows you what to take out of the registry. I did try to do it without making changes to the registry and it still didn't work. Just removing the program through windows add and remove programs does not work. You have to get into the backend and try and remove every trace of Thunderbird then reinstall.

I now have it working properly with the exception of file associations. If somebody sends me a word document it always tells me the splash screen "open with which program" even though Microsoft Word is selected every time. When you go into the program file association defaults it very clearly shows that the relationship is correct between Word documents and Microsoft Word in the same with PDFs and anything else that comes in. In my installation something is not quite right even now.

Everything else in version 91 seems to be working okay (thankfully) I did do a donation after I sorted out getting version 91 to run