I've read that people were having issues with BIAB 2020 and Big Sur with a bug with the lead sheet window.

I am having the same issue: click on lead sheet, opens a full screen blank page. In addition, I can not close those windows. The only way to get them to close is to quit app.

I am on OS 11.2.3, BIAB version 2019 (324). I have checked for updates, but there are none.

I think I saw that there was a patch available but not for 2019 version. Unless I didn't see it.

I also have a strange magenta bar across where the title of song is.