Below is the debug info from the mac crash dialog. I have this error consistently when saving in any format (png, krita, jpeg were all tested). I've attached the file in case it helps. https://docs.google.com/document/d/1a484Lb1D8ZixAOx5FPxkL_EUHBtcgpKGDQ6lPBcyOTo/edit?usp=sharing
This probably is a bug fixed in 3.0.94: https://krita.org/en/