It’s your system and you agreed to licence your data to them. So technically it’s not theft. But also technically, pirating isn’t theft either, you’re not breaking into microsoft HQ and stealing a product key.

On a practical everyday way, yeah, I would say they are “stealing” your data, since they hide that as a clause in a massive EULA that can be altered at any time, and you either accept it or don’t get to use what you bought.

You sign ownership away when you scroll past 35 pages and click “I Accept”