Fwiw, I'm not seeing lag on my end doing the same. Can turn on magit blame and it still scrolls fine. :(
Opening a very large file?
Edit: I have found that if I don't reboot my Mac, the environment that a launcher emacs finds is sometimes off. Is it the same slow if you launch from a terminal versus the dock?
I don't think anyone really wants to profile their editor. That said, if you have the cycles to spare, M-x profiler-start, scroll, M-x profiler-stop may have some obvious culprit.
Opening a very large file?
Edit: I have found that if I don't reboot my Mac, the environment that a launcher emacs finds is sometimes off. Is it the same slow if you launch from a terminal versus the dock?