Unless I’m missing something, shutting down the forum does precisely nothing to limit GDPR liability as the main drone.io site itself has an account/login area. Whilst it’s private beta currently, unless EU access is blocked, GDPR liability will continue to apply to any personal data collected via that.

The only benefit here is that there’s one fewer system to keep track of when it comes to tracking/deleting personal data - the need to respond to subject access requests, right to be forgotten, form letters etc remains.