Howto login into android app DB Navigator

TLDR log in with android browser

since recently I could not log into the app of Deutsche Bahn, DB Navigator, anymore.
If I try to log in, it wants to open a browser. I logged in with the stock sfos browser, but login didnt succeed.
However, if you select fennec or chromium (android apps) in the “open with” dialog it works flawlessly.

(Just noticed this is maybe also a bug report, but I mainly wanted to help others)