Critical error after updating my wordpress

If you are using WordPress 5.2 or newer, then the site should by default send a fatal error notification email to your admin email address.

The email should have some sort of stack trace in it, which shows where the error occured. Then either login to the site using the recovery mode link found on the email or to the server via ssh/sftp and fix the problems.

You can also make WP produce a debug log by turning debugging on in wp-config.php, via ssh/sftp, and reloading the browser page. The log file is created in the wp-content directory and it contains also the stack trace.