wp-admin php commands throwing 500 error

I am pretty disparate here. Things seems to be devolving pretty fast.
After the auto update of 4.7.4, I was having issues trying to do a simple update on a page using DIVI. Every time, I’d update the page, it would revert to the what it was showing before the update.

Then DIVI had a new revision – I thought “Great! they’re responding to this issue”

Then I started getting this message when executing php commands:

“This page isn’t working

xxxx.org is currently unable to handle this request.
HTTP ERROR 500”

https://mysite.org/wp-admin/themes.php – this does not

so I can’t roll back through the interface or disable the child theme

This command works:
https://mysite.org/wp-admin/edit.php

This does not:
https://mysite.org/wp-admin/post.php?post=35752&action=edit

Since I’m on Chrome, noticed that the commands that work have the green secure https and the ones that don’t have a grey i in an circle – meaning not secure.

I saw WP recommends 5.6+ php so I changed to 5.7 on my server. then even https://mysite.org/wp-admin threw the 500 error. So I changed back to 5.3.2.

On Firefox and Safari all I get is a blank screen on the pages I get 500 error messages for.