Can that topic be made a sticky? Common problems while upgrading to 3.3.0
Otherwise, it's not visible to anyone when viewing the support forum - it's the first thing one would look for.
I had a related problem. My passwords didn't work after upgrading PHP to 7.4 because I was missing the PHP sodium module. CentOS and Fedora do not include the sodium module as a default. I asked for help because I didn't know this module was missing.
My support request (with solution) is here: Re: Updating PHP 7.3 to PHP 7.4 login fails with invalid password
I recommend revising the locked topic to add a new section:
Problem: Passwords don't work after upgrading to PHP 7.4+
Newer versions of PHP offer new password hashing algorithms which we make use of. If you upgrade to PHP 7.2, passwords will be hashed using Argon2i. If you upgrade to PHP 7.3+, they will be hashed with Argon2id. PHP implements the Argon2id algorithm in the sodium module.
Some operating systems do not distribute the sodium module as a default.
Solution: Install the PHP sodium module
I also recommend adding the sodium module as a PHP requirement.