errors 404 and error 500

Let’s start with the 500 error.

Errors like this are logged. Check the error log on your server. If you can’t find the log, please contact your host.

Meantime, enable wp_debug and wp_debug_log and after an error, look at wp-content/debug.log to see if anything gets logged there. https://www.ads-software.com/support/article/debugging-in-wordpress/

You can also try this: Please attempt to disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.

If you cannot access wp-admin, there are other ways to deactivate plugins:  https://www.ads-software.com/support/article/faq-troubleshooting/#how-to-deactivate-all-plugins-when-not-able-to-access-the-administrative-menus

Also, 404 errors, might be, that the .htaccess file has been changed/edited and there are some issues with your permalinks structure. In order to resolve the most common issues for 404 errors in pages, go to:

Settings -> Permalinks, and re-save the settings, it will re-generate the rules and update your .htaccess file for you! hope that helps!