Leaving Twitter for Mastodon barely had an impact. I was just about done with that whole place, with or without Musk in charge.
Reddit is different... I still loved using it. I had my subscriptions honed, all my interests represented. I suffered none of the toxicity that others saw. Not sure if that was just because I mostly used smaller, niche-interest subs or because I mostly lurked and seldom posted? It was all friendly, knowledgeable and entertaining, a stream of consciousness that I could dip in to whenever I wanted to.
So I'm not leaving Reddit because of the experience, but more on principal (both the API kerfuffle and a general aversion to ad-revenue models, which are clearly harmful to society). Principals sadly don't give me something to read over breakfast...
I hope Lemmy can become that stream of consciousness in time. I'm trying to do my bit by being an active contributor rather than a lurking grazer.