I’m not sure what you’re arguing here. It’s backwards compatibility if a given version of say, Photoshop, designed to run on Windows N, now runs on Windows N+1 as well… at least from the perspective of the OS, which is what we’re discussing?

It’s forwards compatibility if we’re discussing the idea of the program being compatible with future versions of Windows, but that’s neither the point of what was suggested, nor is it realistic — breaking changes, or compatibility, are going to be at Microsoft’s hands and largely an intentional decision at a platform level, not something an individual developer can shore up against.