I don’t think Reddit being replaced is as much of a given as everyone seems to think. People might simply get tired of the concept altogether. Nobody needs a vote based link aggregator thingy in their lives, and there is no shortage of social media in sight.

I don’t know, but hey you heard about that Ukrainian cat themed dating sim?

Discord

Lemmy, tildes, and arguably pixelfed for those subreddits that were image heavy.

The fediverse has places like https://kbin.social/ or there are instances of Lemmy, (https://join-lemmy.org/instances) but most people will want to avoid the "main" lemmy instances for places like https://beehaw.org/

The main lemmy instance is under heavy load and its admins definitely have their own political slant, and if you're not comfortable with that (most aren't) it's best to find a different one or make your own instance.