There is no supported OS that uses PHP 8.4 as the default, so we have not tested that yet. We will test and support it as soon as a supported OS uses that PHP version. Do not change the default PHP version of the OS!
i changed to 8.4 and it worked i think with one exeption, smth which required lower. my admin set cli to 8.2, seems to work fine 8.4 and cli 8.2
Debian Trixie is 5 days away from general release so there will be a major distro based on php8.4 next week. As you have discovered ISPConfig appears to mostly work OK subject to further testing. But Trixie's Dovecot 2.4 isn't yet supported by ISPConfig so that is a bit of a blocker for Debian 13 until the good folks at ISPConfig can get that sorted. I know, I'm impatient too.
