These are private computers for gaming with Steam installed. This will literally be less than pocket change to them. They likely lose more from pirated Windows and secondhand purchasers of Apple products.

The amount of money tech giants lose will not be affected for a long time. The main achievement for Linux right now would be to get a foothold, to make it known to the public, to normalise its use. The big change will come when organisations start moving to Linux (which you would think would be a priority considering the fact that it is free and more secure).

They make more on cloud servers than as operating systems nowadays.

Till that number starts hitting like 15% because these are just private users. These big companies aren't even going to be able to notice the shift.

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.