Most of my hard science contacts (physics, biology etc) from my days in student government have moved to Bluesky. Newer academics seem to be starting out there and skipping Twitter entirely.
If you have heard of Metcalfe's Law, you'll understand why this is not good for Twitter long term.
It's like internet media is reaching a new level of maturity in that it is bifurcating into the tabloids and the serious magazines, like printed media was before.
Since covid much of the biological academic people on twitter were getting violent threats from anti-vaxxers and anyone angry about science contradicting the proclamations of their deal leader Trump.
Why would anyone with half a brain stay to experience that?
If you have heard of Metcalfe's Law, you'll understand why this is not good for Twitter long term.
[1] https://en.wikipedia.org/wiki/Metcalfe's_law