Where are the official DLSS 4.0 *.dll files for MSFS2020 and 2024?

Nvidia app is not required and in some cases, it may even be responsible for CTDs . So uninstall Nvidia app.

In the linked topic below, I described how to get latest DLSS4 without NVIDIA app or DLSS Swapper.
https://forums.flightsimulator.com/t/nvidia-game-ready-driver-572-16/702204