Visual Studio 2026 upgrade. SynthVoice.h not being compiled

I just upgraded from Visual Studio 2022, to 2026. During installation I selected it should import over my 2022 configuration, however no matter how much I edit SynthVoice.h, or set “Excluded from Build” to “No”, set “Enable Minimal Rebuild” to “No”, “Not Using Precompiled Headers”, and do a “Rebuild Solution”, VS 2026 does not compile SynthVoice.h or any other header file for that matter.

Any idea of how to fix this?