I upgraded my 1.5.2 instance to 1.6-beta. The instance runs on PHP8.0. That worked fine, I could log in, read emails and open the configuration. As the document says the version would be compatible to PHP8.1, I changed the running PHP fpm to 8.1. Now I cannot log in anymore, it says "Die Anmeldung ist fehlgeschlagen." ("Login failed"). In the error log I find messages like this:
PHP Warning: Undefined array key "ssl_mode" in /var/www/roundcubemail/program/lib/Roundcube/rcube_imap_generic.php on line 1053
Reverting to PHP8.0 did not help.
See my last response, issue is solved.