neotheghost if i not wrong, error 500 only occur when you select wrong php version for your sites.
on me, if the php version is like... 5.3 the sites will shown error 500
but when i setting it php 7.4 the website can run without any problem
and also don't forget to restart all. include server, maybe some setting get stucked
last things to do is uninstall nginx, and apache first before you install OLS
from very start using AAPanel i always using OLS XD so that's what i can do when the error appear... if you already have OLS working, i think you shouldn't edited or configure it anymore
because some error will make you do alot of things to fix that
