Hello again,
So I checked which log files were affected when triggering the form for the Auth configuration. It looks like it's the /var/log/httpd/ssl_error_log and shows the following error :
[Fri Oct 14 10:14:14.706167 2022] [php:error] [pid 2091] [client <my_computer_IP>:59183] PHP Fatal error: Uncaught Error: Call to a member function setConfigClass() on null in phar:///var/www/<mysite>/html/include/plugins/auth-oauth2.phar/oauth2.php:592\nStack trace:\n#0 phar:///var/www/<mysite>/html/include/plugins/auth-oauth2.phar/oauth2.php(405): GenericEmailOauth2Provider->getPluginInstance()\n#1 phar:///var/www/<mysite>/html/include/plugins/auth-oauth2.phar/oauth2.php(417): OAuth2ProviderBackend->getConfig()\n#2 /var/www/<mysite>/html/include/class.email.php(567): OAuth2ProviderBackend->getConfigForm()\n#3 /var/www/<mysite>/html/include/class.email.php(631): EmailAccount->getOAuth2ConfigForm()\n#4 /var/www/<mysite>/html/include/ajax.email.php(23): EmailAccount->getAuthConfigForm()\n#5 /var/www/<mysite>/html/include/class.dispatcher.php(151): EmailAjaxAPI->configureAuth()\n#6 /var/www/<mysite>/html/include/class.dispatcher.php(38): UrlMatcher->dispatch()\n#7 /var/www/<mysite>/html/include/class.dispatcher.php(120): Dispatcher->resolve()\n#8 /var/www/<mysite>/html/include/class.dispatcher.php(38): UrlMatcher->dispatch()\n#9 /var/www/<mysite>/html/scp/ajax.php(326): Dispatcher->resolve()\n#10 {main}\n thrown in phar:///var/www/<mysite>/html/include/plugins/auth-oauth2.phar/oauth2.php on line 592, referer: https://osticket.<mydomain>/scp/emails.php?id=4
I also already tried to remove and reinstall the plugin, it still does the same.