We are having problems as well, both in our production environment and in a freshly installed test environment. I have followed the official instructions to the letter: https://docs.osticket.com/en/latest/OAuth2/Microsoft%20Authentication%20(SSO)%20Guide.html
But when I try to log in as an agent, authentication is successfull (it shows up in our Azure portal logs) and I'm redirected back to the default osTicket homepage. When I try to access the admin panel, I'm not signed in.
We are running the latest osTicket version and OAuth2 plugin on a freshly installed IIS on a fresh Windows Server 2019, php version 8 and MySQL version 8 aswell.