Most of the uses for a casual computer user have been replaced by smartphones and tablets.

Then you have walled gardens like the Apple ecosystem where interoperability is superior among Apple products which cross sell each other. If you got an iPhone, now get the Apple Watch and a Macbook and all integrate well.

Then you have games, where consoles will give you a decent experience for less money.

Then you have professional users where the most common use case is office documents. This remains contentious but there are more alternatives now like web apps, MS Office clones like Libreoffice, Softmaker Office/FreeOffice, WPS Office.

Then you have specific desktop apps for specific OSes and there you are tied to an OS. This is one of the few legitimate uses for Windows I can think of.

Otherwise Linux is king.