Hi!
Thanks for your post and sorry for the trouble!
Can you please clarify where you are getting this error? The 500 error probably shows up as an error right below the “Save Changes” button, right? However, that other piece looks more like an error from the browser’s error log console in the developer tools? I’m not sure that this is (directly) related.
It would be good to maybe get more error information from the server. For that, please set the WP_DEBUG constant to true in your site’s “wp-config.php” file, see https://developer.wordpress.org/advanced-administration/debug/debug-wordpress/#wp_debug , or maybe check the server’s error log file (if you don’t have access to that yourself, you web host company’s support team should have access).
Regards,
Tobias