[DiscoBahb]

Repeat after me: Flat bands do not imply superconductivity. DFT calculations cannot be used to predict superconductivity. DFT is a single-particle calculation. Superconductivity is a multi-particle phenomenon.

At most, the preprint(s) you're referring to suggest that maybe (under their unverified assumptions) electron-electron interactions could lead to interesting physics in that material. It provides no evidence for what that physics looks like and says nothing about what temperature these things will occur.

High temperature superconductivity is not well understood and we do not have the theoretical tools to make quantitative predictions about it. At best we run dodgy simulations, squint at the resulting plots, and say "hm, that's interesting".