For me, the answers are:
- Facebook. Sigh.
- Reddit, but 90% of my activity is reading and the occasional comment
- Tumblr
- Mastodon
- Bluesky is a distant fifth
I don’t like Discord, so I decided to drop all the Discords I participate in. If those communities go to a proper community platform, I’ll gladly rejoin.
I do LinkedIn for professional reasons.
I don’t do Instagram and Threads now, but I might go back.