Long story short, a few days later and went back to my old habits... Magisk, Kernel, you name it. And the banking app stopped working again.
I do pass the safetynet test, have repackaged Magisk Manager. Google Pay is working like a charme. But Fidor bank seems to be better than Google, at least in this regard. I tried logging traffic using adguard, the app does not connect to anything, no dns requests as well.
Most of the times the app won't start at all, sometimes the first screen flashes for a very short period, and sometimes chrome opens with a webpage from the bank telling me my device is modified. How the **** do they know?
Maybe you guys may have a hint in what direction I could continue poking, because carrying a second phone just for banking is a little bit overkill...