Yes, the new generation Firefox for Android only features selected recommended add-ons. You can install them from the menu, either:

• menu > Add-ons
• menu > Add-ons > Add-ons Manager

For Nightly, it's a little complicated. Please see this blog post: https://blog.mozilla.org/addons/2020/09/29/expanded-extension-support-in-firefox-for-android-nightly/

For Nightly, it's a little complicated. Please see this blog post: https://blog.mozilla.org/addons/2020/09/29/expanded-extension-support-in-firefox-for-android-nightly/

So if I install Firefox Nightly I can use any addons listed on AMO as long as I add them to my collection? Do you know in which version it was implemented? Because honestly there is no reason for me to use Firefox on Android if I'm restricted to 11 (XD?) addons

I don't know when it was implemented, but presumably around the time of that blog post. I haven't tried it myself.

I tried it on Nightly and it works as intended

Suprisingly it turns out that you also CAN install addons from the AMO site if you choose the "Download file" option instead of the greyed out "+ Add to Firefox" button, even if the addon is not on the "recommended" list

I have no idea why it isn't mentioned anywhere that you can do that, or why is the "Download file" button so small, but it solves the problem