People always seem to miss the point. Saying an OS or a platform is “dead” doesn’t mean extinct like the dodo bird. So if your mom has a windows based PC in her sewing room - that does not refute the stated argument.
“Dead” here means - not what it once was - no longer the 900 lb. gorilla that gets to control how the game is played.
Think of Network News. It still exists - sure - but it ain’t what it used to be. This is the way to think about articles such as these.
Maybe another example is Blackberry. You can still see these around from time to time. But they eventually will become an historical footnote. But 5,6,7 years ago they were poised to take over the world.