I am still not having any luck. I have restarted my phone. I have uninstalled, reinstalled Facebook and messenger and did a hard reset on my ohone and it still crashes. I have a feeling that Facebook and messenger are not optimized for the Galaxy s21 at all. I have also reached out to Facebook as well as Samsung about this issue in hopes that someone will do something.
Good news. There's a phone software update from Samsung that just dropped in the last few hours. Hopefully this solves the problem. Downloading now.
Unfortunately even after the new update I had FB messenger randomly close a couple of times while trying to reply to a message. So problem is still not fixed.