What you’ll need

You don’t need to reach wp-admin to fix a broken plugin. The file system and logs are enough. “There has been a critical error on this website”

Steps

Step 1: Check for the recovery email
Look in the admin email inbox for ‘Your Site is Experiencing a Technical Issue’ and use its recovery link if present.
Step 2: Enable debug logging
Edit wp-config.php: set WP_DEBUG true, WP_DEBUG_LOG true, WP_DEBUG_DISPLAY false. How to turn on WordPress debugging safely
Step 3: Reproduce and read the log
Reload the site, then open wp-content/debug.log. Find the PHP Fatal error line and the folder in its path.
Step 4: Disable the culprit
Rename that plugin’s folder in wp-content/plugins (or theme in wp-content/themes) by adding -off.
Step 5: Confirm the site works
Reload the front end and log in to wp-admin.
Step 6: Resolve properly
Update, replace or reinstall the plugin, or restore its previous version. Then rename the folder back if you’re reinstating it.
Step 7: Turn debugging off
Set WP_DEBUG back to false and delete debug.log.

The site and wp-admin load, the faulty component is updated or removed, and debugging is switched off.

What happens	What to do
No debug.log created	Check the domain error log instead. How to find PHP errors (error logs and display_errors)
Error points to wp-includes	Core files may be damaged; re-upload WordPress core, excluding `wp-content`.