There is also a Germany-specific app called Luca:
luca - Apps on Google Play
I’m on iPhone not Android, it‘s in the Australian iOS App Store but I don’t know about the Android one, but if you’re on Android try that link and see.
If you can use it, it’ll get you into anywhere in Germany.
Side note: at Toulouse (France) the customs official didn’t scan the code or enter it, didn’t look at the test result printout I had ready, just glanced at the paper certificate and waved me on. I was surprised but didn’t argue (it was Christmas Day mind, that may have had something to do with it
.