I'm using a standard USB keyboard with my MacBook, added a custom keyboard layout (in
Library/Keyboard Layouts) and it works fine, but mac OS keeps switching back to the default layout after a few minutes.
update: I just noticed that it switches when I focus the Microsoft Outlook App. Strange. Sadly setting the language of outlook to English doesn't solve that.
I tried deleting the file
Library/Preferences/com.apple.HIToolbox.plist (as suggested in similar questions) but it didn't help.
I'm currently running Catalina 10.15.3