This was my first time seeing this error on one of my wordpress sites. Before I got this error I was seeing a NGINX error and didn’t understand why because all the other sites on this server was still up. I logged in and edited my NGINX file to use php8.0-fpm instead of php7.4-fpm. I reloaded and then went back to refresh the site. That is when I saw the error message:

There has been a critical error on this website. Please check your site admin email inbox for instructions.

I turned on debug by editing the wp-content file and turning debug to “true”. I saved it and refreshed the web page to get a message about a specific plugin. The directory was called anti-spam but I think it was Titan Security. I deleted the plugin directory and then refreshed again. That allowed me to login.

I should also mention that when you are switching PHP you also have to install the newer versions of cURL and ZIP. At least everyone should be using them in their wordpress installs. sudo apt install php8.0-curl and sudo apt install php8.0-zip.