The service file for apache2 with systemd sets the NoNewPrivs flag to true, which breaks suexec.
Perhaps it can be set to false if [suexec] is set.
I also have [suexec-caps] set true. I'm not sure if this is part of the issue.
Any logs you can provide, or similar...?
As of right now, you will get this in your suexec log (and get 500 errors):
[2020-10-20 13:37:18]: failed to setgid/initgroups (1000: php): Operation not permitted
Updating the service file and changing
and restarting apache fixes it.
If there's a more secure workaround it's probably preferable.
*** This bug has been marked as a duplicate of bug 600292 ***