>Can anyone tell me why since past version 68 of Firefox on Android nearly all my add-ons don't work
Because they switched rendering engines or something. Now addons are restricted to a small subset that they've validated. You can use a custom addon collection to install untested addons (see: https://blog.mozilla.org/addons/2020/09/29/expanded-extensio...) to get around this, but there's no guarantee that the addons will work.
I can confirm the add-on I Don't Care About Cookies works just fine if installed that way. It's just inconvenient. I wonder what stops the list of approved add-ons from growing.
Because they switched rendering engines or something. Now addons are restricted to a small subset that they've validated. You can use a custom addon collection to install untested addons (see: https://blog.mozilla.org/addons/2020/09/29/expanded-extensio...) to get around this, but there's no guarantee that the addons will work.