I have a different experience. Some of my fandoms still have plenty of activity on Tumblr, but there's at least two where people rarely share any fic and art outside the locked down discord, and this is because the harassment towards authors and artists of publicly posted works has gotten so, so bad. I'm not surprised that things have moved in this direction. I'm glad ao3 has an anonymous option so some people are still willing to post some things for lurkers outside of the discord community, but I also understand why a lot of people don't.
Re: OT Thread (Other fandom salt)
I have a different experience. Some of my fandoms still have plenty of activity on Tumblr, but there's at least two where people rarely share any fic and art outside the locked down discord, and this is because the harassment towards authors and artists of publicly posted works has gotten so, so bad. I'm not surprised that things have moved in this direction. I'm glad ao3 has an anonymous option so some people are still willing to post some things for lurkers outside of the discord community, but I also understand why a lot of people don't.