Yeah, that’s what I was thinking.
I’ve deleted the build_darwin directory and tried to rebuild many times. Didn’t help.
The SDK seems properly installed. The SDK files (cmath, fstream, etc.) are all present in /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/c++/v1. And their contents also seems fine.
I created a little CPP demo console application that uses cmath and fstream and get the same “file not found” errors while building, both using a “simple” build and using CMake. There must be something wrong in my environment that causes it to not resolve these files. I will investigate further…