I mostly agree on the VSCode part. They should put it up front in the README, homepage and maybe a info modal/badge whenever a user installs said extension.
But genuinely asking, how else would you 'label' VSCode?
"A free and open-source code editor with some optional components that are proprietary"?
Apple is worse in that regard. Is XCode open-source? Other than Darwin Kernel, is any part of macOS open-source? Did Apple even try to make Swift cross-platform? Is iCloud really comparable to OneDrive? How about Apple's locked and closed-source bootloaders?
As a consequence, many Swift libraries only focus on macOS, just like many dotnet libraries focus on Windows (though recent efforts have improved that situation). You can probably get a lot of them working on Linux as well and if you use Swift for command line tools or web applications. I suppose you can probably run the most important tools cross platform, but the non-native ecosystem is clearly a second class citizen.
The big difference between XCode and VSCode is that Apple doesn't claim XCode is open source; also, XCode is more comparable to Visual Studio than VSCode in terms of SDK integration and preconfigured tooling.
Huge parts of the Darwin kernel are actually publicly accessible while Microsoft only provides kernel sources under NDA in things like education projects. Unless you count the WinXP source code leak, that is.
C# is sort-of mostly open source-ish except that debugger features are closed and the community has little say in its development.
Apple did in fact put effort into making Swift cross platform, as outlined here[1]; though their intention is that Swift programs use the system runtime on macOS/iOS/iPadOS, they put the effort into making a base layer freely available for other operating systems to gain some portability.
I'd personally argue that Apple and Microsoft are similarly if not equally open in their development, but Microsoft advertises itself much more "open source" than Apple. Apple's approach of "you can look but you can't touch" is a lot more explicit and their supposed openness comes up in fewer marketing materials.