Sadly I haven't seen any active communities here on Lemmy; Reddit has/had one (I haven't checked in on them in a long while though). As to what resources you would need for a refresher, I'd recommend something like Wheelock's Latin Reader, which is full of adapted and original texts to get you some practice. As to the grammar side of things, either a formal reference grammar like Allen and Greenough's or Bennet's. If you want something more structured, I'd recommend a collegiate textbook, such as A New Latin Primer (I use this with both my collegiate and (upper-level) high school students). Lastly, if you'd like some bite-sized refreshers on specific topics, Latin Tutorial on Youtube is a good resource. Hope that helps!
Edit: Turns out Bennet's grammar is available at the Latin Library: https://www.thelatinlibrary.com/bennett.html