Can't use iostream as module in C++20 (Win10 Clang)

Question

I am not being able to import iostream on Clang 13.0.0 under a Windows environment, obviously neither compile with this command line:

clang++ --std=c++2b -fmodules main.cpp -o main.exe

I am perfectly able to use it under an Unix env. Looking in the Clang include folder, there's no such header file in the W2 installation.

Have someone idea of what's the difference with the Unix installation, and how to solve it?

Thanks