Can't open config page

Your software
My Mautic version is: 4.4.0
My PHP version is: 7.4
My Database type and version is: 10.6 Mariadb

Your problem
My problem is:

Everything works on my Mautic, but config page doesn’t load.

The system gets busy, then 502 not found.

These errors are showing in the log:
No errors at all! That is the problem.

Steps I have tried to fix the problem:
mautic upgraded from 4.2 to 4.4
mariadb upgraded from 10.4 to 10.6
permissions okay
users are fine
cache cleared
assets rebuilt

Check httpd error log on server if you have access to it.