It seems, that Tooltips is not ready yet for PHP 8.1.22:
Frontend - Error:
0 in_array(): Argument #2 ($haystack) must be of type array, null given
/home/httpd/vhosts/domain.ch/httpdocs/plugins/system/tooltips/src/Data.php:123
I don't see how that error can show up. Maybe some of your files did not overwrite correctly on installation.
Can you give me (super) admin and (s)ftp access so I can take a look?
And tell me on what url I can see/reproduce the issue.
You can use the 'Confidential information' button in the forum editor to hide sensitive information.
I send you the information. Everything is fine at the moment (PHP 7.4). Let me know when you want me to switch to PHP 8.1 so you can see the error message.
Thank you.