When critical errors occur, they’re often logged, which can help identify the cause. You can enable debugging in WordPress to gather more information. To do this, add a few specific lines to your wp-config.php file. For step-by-step instructions, refer to: https://developer.www.ads-software.com/advanced-administration/debug/debug-wordpress/
Another troubleshooting step is to disable all plugins and switch to a default theme. If this resolves the issue, you can then reactivate plugins one by one to pinpoint the source of the problem. If you’re unable to access the wp-admin dashboard, follow this guide to deactivate plugins manually: https://www.ads-software.com/documentation/article/faq-troubleshooting/#how-to-deactivate-all-plugins-when-not-able-to-access-the-administrative-menus
Finally, consider restoring a backup from when your site was functioning correctly. This can be a quick way to revert any problematic changes.