I left sdf.org because it was too slow and sometimes down. I went to mathstodon.xyz because it seemed appropriate but I admit I didn't really look very carefully. Hopefully it's well-run and backed-up.

https://mathstodon.xyz/about

The actual topicality of an instance isn't too important to me: I don't look at local timelines. It's more signalling my interests. I don't post often enough to be annoyingly off-topic - hopefully.

@nprofile1q... @nprofile1q...