hmm, mail is fine here. have you tried booting into safe mode, and opening mail there? then rebooting normally..
Thanks! Tried that, seems the same. Somehow it feels like there's a lag after every keystroke, especially when using the arrow keys just to select items in the Message List. 2019 MacBook Air, seemed fine before Big Sur. Not the end of the world, but disappointing. Just not snappy like before.
how does the menubar affect you seeing multiple open windows? the text & icons are perfectly visible on the menubar; perhaps try a different wallpaper? just a thought...