Not really sure what all I did at this point. Restarted services and the server itself it a few times during the process... to no avail.
Noticed it still showed 8.1 even though I installed PHP 8.2... ended up reinstalling libapache2-mod-php... which worked but installed a minimal 8.3 instead.
It's working now after installing all the 8.3 libs I needed.
That said... The OAuth authorization process is a little different now... I thought it was failing because it didn't show the same auth page from o365 and returned to the admin panel quickly... but I checked and it had a valid token so it worked.
Then it took about 5 minutes before it emptied the helpdesk email box. But it is working now.