A techie post for you on a Saturday evening…because when I run into these issues…it is good to document them…for me and for my technology / WordPress readers.
If you run into a 500 Internal Server Error on your WordPress site…here is where I recommend you start (fix via wpbeginner):
Checking for Corrupt .htaccess File
The first thing you should do when troubleshooting the internal server error in WordPress is check for the corrupted .htaccess file.
You can do so by renaming your main .htaccess file to something like .htaccess_old. To rename the .htaccess file, you will need to login to your site using FTP or File Manager app in your hosting account’s cPanel dashboard.
Once you connected, the .htaccess file will be located in the same directory where you will see folders like wp-content, wp-admin, and wp-includes.
Once you have renamed the .htaccess file, try visiting your site to see if this solved the problem. If it did, then give yourself a pat on the back because you fixed the internal server error.
Before you move on with other things, make sure that you go to Settings » Permalinks page in WordPress admin area and click the save button without making any changes. This will generate a new .htaccess file for you with proper rewrite rules to ensure that your post pages do not return a 404 error.
If checking for the corrupt .htaccess file solution did not work for you, then you need to check out this website for additional solutions: https://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/comment-page-5/
Not how I want to be spending my Saturday evening…but always happy to find a quick solution that works the first time. Hopefully it works for you as well if you run into this situation.