This error can have multiple reasons to appear.
Resolving 500 errors - general: this error can only be resolved by fixes to the Web server software. It is not a client-side problem. It is up to the administrators of your Web server site to locate and analyse the logs which should give further information about the error
So the best I can suggest you is to contact the hosting company and see if they can fix this issue.
On top of that, do you know or can narrow down if you did any modifications that might have caused the error?
Custom core files modifications, plugin installs, etc.?
I would recommend to go to the hosting server > wp-content > plugins and delete (move) the plugins one by one.
You could also check out for .htaccess issues. 500 errors can frequently occur with incorrectly configured rewrite rules contained in your “.htaccess” files, so you should probably try removing those from your folders to see if it’s the cause. Keep a backup of those files of course, you might still need them.
If nothing works and considering actual WordPress pages still come back with error 500, that would certainly indicate that there’s something wrong with your WordPress installation. It might be worth trying to install a fresh new installation, and restoring your data from the old one.
Take a look at the backup instructions docs for help. This also contains some instructions for restoring the database back into a clean installation.
Don’t forget that you will not only need to restore the database, but also any media, plugins, and your theme in the “wp-content” directory.
I hope this helps you with the debugging, there’s not much I can do about it since it does not seems to be a theme related error.
Keep me posted about the outcome.