I’ve come across a bug that I want to bring to your attention. I’m using an iMac with macOS Big Sur 11.0.1 and running the latest AppStudio 220.127.116.11
I can reproduce the bug every time as follows:
Open or create a blank project and drag in two BS4 labels.
Select one of them and click on the ‘appearance’ field in the Properties section (under ‘Common’) and then on the dropdown icon so that you have the list of options showing.
Without closing that list (i.e. with the dropdown list still visible), click on the other label in the Project Explorer section above. AppStudio will immediately close and a standard Apple Problem Report will pop up to send the report to Apple.
Hope you can fix it.