I really can't tell if it is the same situation bolandross is having. From my many issues with BIAB's UI, it being sluggish is not one of them.

I confirm that I've been having this situation since I first installed BIAB (2018) and through out all MacOS releases since then.

Alternating to full-screen chordsheet mode doesn't make a difference.

Default synth is indeed Apple DLS Music Device.

In order to test it at factory settings I need further help. I couldn't find a file named safemode.txt.