The original permission was fine as mentioned before, never change that to 750 as you open up a security hole by doing that. The permission errors shows that PHP seems to run as wrong user and group. Check that the suexec module is installed and working on your system. You might also want to try to put a PHP file with phpinfo() function inside into the folder /usr/local/ispconfig/interface/web/ to see which PHP version and which PHP handler it shows. Not that you switched to mod_php now.
I stuck an info.php file in that directory and looked around. PHP Version 7.4.20 Directive output_handler lists "no value" for local and master. I've seen this empty on other servers so I don't think that's the correct entry. What directive am I looking for?
I nuked PHP. Code: yum remove php* yum remove php Then went back to the Perfect Server instructions for Centos 7 and reinstalled according to the instructions... and it works! Must have been an additional php module. I'll have to reinstall other packages carefully to be sure I don't accidentally install a module that's breaking PHP.
