I tried with 8.0 and 8.1. My mistake I reported the error using 8.1.
Using php 8.0 I see:
We were unable to start a PHP session. You will need to contact your host to adjust your PHP configuration before you can continue. The error reported was: session_start(): Failed to read session data: files (path: /var/cpanel/php/sessions/ea-php80)
Using php 8.1 I see:
We were unable to start a PHP session. You will need to contact your host to adjust your PHP configuration before you can continue. The error reported was: session_start(): Failed to read session data: files (path: /var/cpanel/php/sessions/ea-php81)
However the host insists that everything is working fine on their side. I think in order to see the forum again I can only restore from a backup. But how to do then for updates, which require a minimum of php 8.0 ?