I run a Mastodon instance. I strongly dislike the v4 redesign, so I stick with the v3 branch for now. Unfortunately, there will be a day they stop maintaining v3, so I'll have to update to v4 if I don't want to be stuck with known security vulnerabilities. Maintaining a fork isn't an option because even a small patchset like glitch-soc takes a lot of work to keep updated.