95% of what I see many ordinary users do with a computer these days is mediated from within a browser window (Chrome, Edge, Safari, Firefox). Those browsers seem to work just fine on MacOS or a Linux desktop.
The point isn't what's possible, it's about the way things are now. Most people with a desktop or laptop machine run Windows on it. Could Linux do everything they want from a computer? Sure, almost. Are they actually using Linux? No - ergo, Windows is still massively important. Not to mention the countless organisations whose IT departments are heavily invested in Windows desktops and all the related supporting infrastructure. Of course they could all change, but they're not going to do it any time soon. Yes Linux is awesome and everywhere but, for example, just a few weeks ago one of my (software developer!) colleagues scoffed when I mentioned Linux and asked if anyone still uses it - while Linux silently runs almost everything around us, Windows is still much more visibly present in most peoples' lives.
