This isn't massively new either:

https://en.wikipedia.org/wiki/Active_Desktop

Active Desktop was always optional, wasn't it? And was it really used for advertising by default? I thought it was mostly arbitrary browser windows that you could attach to the desktop.

Active Desktop was on by default in Windows 98 and had channels from content partners that pushed to the desktop.

No. This was something that your PC manufacturer might have done after an install but not by default when installing from scratch.

Also, a completely different thing entirely.

It's both. Having ads on some apps doesn't make it not an OS anymore. I won't deny it's an advertising platform, just like android or ios or television or radio or the internet. And while it's equally annoying on all those media/systems, it doesn't lessen their or usefulness

There are ads in the Windows UI. I've been an iOS user for 9 years and can't recall seeing an ad in the OS. So it does not seem "just like" iOS, at all.

Music has started showing Apple Music ads, and Apple has also advertised its News app with a push notification on one of my devices.

The fact that Apple Watch has its own pre-installed app feels like an ad to me as well.

And don't get me started on App Store ads... https://twitter.com/nuthatch/status/879783700279418881

I've heard this but I've not yet seen these UI ads people keep talking about. Are they in pro?

Not sure iOS belongs on that list.

I'm not a user, but I assume ads exist in some IOS apps?