500 Internal Server Error!

Hmm, other than really low memory resources the only thing I can suggest is checking your server file permissions and maybe also try reinstalling WordPress.

You can try enabling debug logging -> https://codex.ww.wp.xz.cn/Debugging_in_WordPress

// Enable WP_DEBUG mode
define( 'WP_DEBUG', true );

// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );

// Disable display of errors and warnings 
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );

// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
//define( 'SCRIPT_DEBUG', true );

This would be placed in your wp-config.php file just before the “That’s all, stop editing!”. The log can be viewed inside the /wp-content/ folder.

If you’re not seeing errors there then you’ll want to check your server logs which should definitely show 500 errors and could also hint at where the issue is. The 500 is likely being generated by the php module so you’ll need to make sure that the php.ini also has logging enabled.

display_errors = On

Could be a firewall modsecurity misconfiguration.
Contact your provider and open a ticket on it, they will surely help you.