Use the bleeding edge from the GitHub Master as it has many PHP 8.x fixes.

So I was able to get the login screen to work by replacing the session.inc with the one on GitHub Master.

But now I have this issue Topic: login repeats with every click  (https://frontaccounting.com/punbb/viewtopic.php?id=9606)

I did this per your other post but still doesn't work. 

effective workaround to use the newer commit only for https and not for http:

Replace hardcoded line 14 of includes/session.inc:

define('SECURE_ONLY', true);
to be

define('SECURE_ONLY', (parse_url($_SERVER['REQUEST_URI'], PHP_URL_SCHEME) == 'https'));
This way newer installs will not break when not using https. The last few times, the released versions seem to have some showstopper for existing users. This will only make existing users especially on legacy systems not to upgrade as that would warrant "consultant costs". FA should herd and retain it's flock as that is where the network wealth of the project lies - bulk satisfied standard users who can upgrade atleast in minor versions safely.

I uploaded  my session.inc file maybe I did something wrong.

Also if I downgrade to php 7.4 this repeat login does not happen, only happens with 8.0, 8.1 and 8.2.  I would stay at 7.4 but my hosting service is upgrading everyone to 8.2 in a few weeks. 

Thanks.

When I install a new instance of FrontAccounting on a 8.0+ it works.  But I can't seem to restore any data so that will not be the solution.