How to display a "500" error on a direct transition through .htaccess with your own text?

Question

htaccess

Hello.
Please tell me the rule for .htaccess.
It is necessary when users go directly to the site, display a 500 error to the user with their own text
. For example, "500 error, everything is fine"
But at the same time, show the site to google and Yandex bots without displaying this message
. And if a user enters from Google or Yandex search, then redirect him to subdomain?