For me, the content created by communities that is exclusively available on that site is really helpful to me. If possible I would definitely try and archive a few subreddits and write something to search and access it offline (sorta like https://en.wikipedia.org/wiki/Kiwix but for reddit).
There’s a couple of D&D communities up already, but not as many as were on Reddit. You would have liked r/DMAcademy, maybe.