First, anything but medical masks are not allowed (e.g. cloth, impov etc.).
Only medical masks are allowed.

Then, the regulations differ from Land to Land. Germany is a Federal state same as US and laws are different.

In many states, in public transportation you are legally required to wear a FFP2 mask.
However, I never seen and never heard about anyone enforcing this law.
Even if they would, I expect they would be very kind and you go ahead with a warning.

But again - half of people are wearing normal surgical masks despite the clearly stated rule for FFP2 and there is no punishment to such a behavior.

No mask - it's a big no no, please don't try that.