While it's not 1 to 1, mastodon seems to always be getting mentioned with businesses abandoning Twitter and moving there. I use it but it's just not the same experience
I've checked it out, but was never a twitter user anyways, so I'm not the right audience. I think the lack of an algorithm really hurts the experience for many users. Seems like you have to put work in to get your feed right. Also, the network effect Twitter has is strong. Mastodon is probably the least toxic social media I've seen though.