I am facing similar issue.
ubuntu 18.04.6 LTS
Plesk Panel 18.0.49 Update 2
osTicket v1.17.2 (8fbc7ee)
When I click submit I get redirected to Microsoft's Login page and after I login I get redirected to the osTicket client homepage. If I play around with PHP versions or settings in Plesk such as CGI Application, FASTCGI Application, FPM application etc, either I am redirected to the client home page or i get "input file not specified".
I have already ensure that my httpd.conf file includes the AllowOverride All option.
Also url rewrite is installed and active.
Have already ensured that Oauth2 plugin is the latest version, have deleted the email and re-added, delete the plugin, deleted the email and readded from scratch pretty much everything I found on the forms but am not getting passed this point.
Please help in resolving this.