Someone recently asked if there was a neat way to see where all of the now broken down subreddits moved.
Some moved to Discord, some to Lemmy, and some are somewhere else.
This seems to be a good place to find your communities again: https://sub.rehab/
In the submission process, as well as in the search UI, you can designate if the new community is “Official”, in that the migration was sanctioned by the leaders/majority of the previous community.