If it’s a header, you necessarily can’t. Header gets included every time you want to compile code that depends on a header.
Compilers may offer precompilation etc but if the code you want to change has direct dependency to a large header you need to recompile all of the dependencies.
This is one of the painpoints C++.
C++ modules are here, unfortunely outside VC++ and clang latest, plus MSBuild or CMake/ninja, they are not an option.
The reason why this is taking such a long time is because the entire approach is a rather drastic change to how C++ compilers usually work, and C++ compilers (or even frontends, such as the stuff used by IDEs) are complicated things that aren't trivial to make major changes to.
Wasn't support for submodules first added to Clang and CMake?
Also, I don't think you fully grasp the scope of this change. Some projects are still stuck on C++1 to avoid having to pay for the technical debt of upgrading the compiler. This is a flag flip away.
For modules, you need to rework your whole build system and Eve rearchitect your projects.
Think about that for a second.
VSCode is never going to be as good, you are better of with Clion then.
As win/mac user Visual Studio is my preferred tool, but in MacOS Clion (with vscode for few random workflow things not supported in Clion) is an adequate replacement (but Visual Studio remains king).
VSCode can be used as an industrial editor if one likes to, but if it does not feel right, it’s not a skill issue.