If you stretch the definition of "personal computers", Apple actually has about 45% of the market in the US. Microsoft only has 30%.[1]
[1] https://gs.statcounter.com/os-market-share/all/united-states...
[1] https://gs.statcounter.com/os-market-share/all/united-states...
My smart fridge also has a powerful ARM CPU and a touchscreen and a modern OS. Is it also a computer? Can I use it for productive work? Doe every wearable and IoT device qualify as a "computer"?
So sticking back to general purpose computers that are not locked in a vendor ecosystem and let you install and run whatever you want from whatever sources, Apple is less than 10%, so yeah, with ~80% marketshare Microsoft is basically a monopoly in that space.
I wouldn't.