Apple probably isn't seeing it as a factor. Anyone switching from MacOS to Linux on Apple hardware has purchased Apple hardware and will likely continue doing so because they're the kind of people who buy Apple products and you can't change that about a person.

Of those Windows users switching to Linux, how many of them have decided to stop using a Windows license they've had for years? Instead of upgrading to 11 for free, they're switching to Linux? Or, how many of them are rocking the Activate Windows watermark? There's probably a pittance or two lost in ad revenue, but Microsoft almost isn't a B2C company anymore.