The Drafts TestFlight beta program is re-opening after being reset recently.
If you are interested in testing the latest features, details on signup are at the link below.
Please read all the details on that page regarding beta communication and requirements
Still openings? When I click the Join macOS TestFlight link, all I get is “The Developer removed you from the test program.” Never mind. I installed the App Store version, then quit TestFlight and tried again at which point I was able to join.