KfW55 with 36 cm brick (im)possible?

That doesn't matter. T8 / T9 filled or unfilled always has the same U-value. Only the sound value changes.

It will now also work with KfW55 and 36 cm masonry walls here.
Masonry on the ground floor and attic requires λ=0.07 - probably filled brick or aerated concrete.
Windows Uw 0.9.
Roof insulation must be a total of 32 cm...

What do you think, is KfW55 with gas heating achievable only through insulation and [Kontrollierte-Wohnraumlüftung]?

I don't believe so, or rather, the additional investment will not be in any proportion to the "better" conditions. At least with the current interest rates.

I was told that KfW55 can only be achieved with renewable energies. With gas, you are automatically excluded. My info.

Yes, the "nonsensical" panels on the roof have to be there.