That’s funny - fellow German here, also using macOS with ISO DE keyboards and running into the exact same issue with Karabiner elements. Sometimes keyboard work out of the box, sometimes I need to swap < and ^, sometimes the keys are swapped on the internal keyboard even though I’ve only applied the key swaps for specific devices.

So far I haven’t really cared enough to figure out what the problem is and just remap whatever’s wrong in Karabiner directly, but I would also like to know how to fix that.