Currently VCC supports Windows only. But some Quest players may have only Mac or Linux PC instead of Windows PC. They can upload contents by VRCSDK and some stuffs, but they will not able to take advantage of VCC. So I think VCC/VPM should be cross platform apps.
VCC/VPM base stacks are Unity and .NET 6, so it looks that making cross platform is easier than native stacks. (Sure, I actually know making cross platform apps is not easy. But they will need VCC.)