Critical error

You should first check your hosting to see if there is an error log that indicates the cause of the error. Depending on the hosting settings, this may already be helpful. Often you can already see the name of a plugin in the message, which you can then remove. How to do this without accessing wp-admin is described here (aka deactivate all plugins via FTP): https://wordpress.org/support/article/faq-troubleshooting/#how-to-deactivate-all-plugins-when-not-able-to-access-the-administrative-menus

If the log file doesn’t show anything, you could also activate the debug mode in WordPress. Then the actual error message should also be visible in the browser. How to do this is described here: https://wordpress.org/support/article/debugging-in-wordpress/

What was the reason? You are welcome to set the topic to solved if everything is OK now.