There have been Linux distributions certified as Unix in the past.
When people say "Unix", they usually could care less about certification.
I'd still say that BSDs are Unix and Linux isn't due to, say, kernels of Solaris and FreeBSD having some traces of similar architecture, while Linux is a completely different thing.
Mainly because Windows has more support. Software availability is the biggest draw to Windows. I would quite happily drop it in a heartbeat if Linux came close.
MacOS has no proper UI scaling for example. Something windows had for... I don't know, ever? It was never an issue for me.
For MacOS you need a little extra tool you stumble upon after hours of debugging that teels your MacOS what resolutions your display actually supports so MacOS grants you the option of your desired HiDPI resolution.
It's stuff like this that drives me mad when dealing with the fucking Mac I am forced to use at work.
There is always going to be pros and cons when it comes to UI. Since Mac comes with a set size monitor, I can understand why there is little support for it. Although, as someone who needs PC glasses, it is a big remiss to not cater for disabilities.
As in my other comment, the display menu in settings has options titled more/less space which increase or decrease the size of text and windows on screen, this is accounted for.