So I would guess the problem is WinUI3? I develop Windows GUI apps for fun in my spare time -- I've built some pretty big and complicated ones using WPF/C# and the issues described by the OP don't seem real. My machine is old as hell and my build times are mostly unnoticeable, for example.
I think the worst offender is the new packaging system used by WinUI3. The default project template creates a solution with 2 projects, the windows app itself, and the package. They including .NET runtime into packages, but for some reason VC++ runtime, and WinUI3 libraries, are shipped separately as OS-wide redistributables. Despite .NET compile sources into CPU-agnostic MSIL bytecode, the final result, the *.msixbundle file, contains an independent package for each CPU architecture. Unless touching checkboxes in VS during publish, gonna be two of them, Win32 and Win64.
> I've built some pretty big and complicated ones using WPF/C#
I do that too for living, WPF is awesome in comparison.
