I just installed https://github.com/patrick-zippenfenig/us-with-german-umlauts since I kind of need it because I am used to it. It works perfectly fine, as long as my mouse´s focus is on the MacBook´s own display. It stops working as soon as I am working on an external Display (Samsung 5K G9 if that matters).
This behavior applies to both, the MacBooks own keyboard as well as my bluetooth external one.
It is a MacBook Pro 14" with Monterey 12.0. Also, I noticed that my keyboard icon isn´t working on the top right. So it looks like I got two Keyboard Layouts set up, depending on the display focusd.
Does someone know how I can fix this?