It searches for the patterns @user, user@host.tld and host.tld/@user in the screen name, description, location and URL field. It displays them to you in the correct format for easy copying as well as a CSV download that can be imported to #Mastodon.
It didn't at first when I tested it today, but after seeing that the old version (https://fedifinder-v1.glitch.me/) works, I gave it another try and it went through. Down to 538 from 617 accounts. Will have to look into what happened with the rest (deleted?).
#Debirdify sadly got suspended by Twitter last week.