Windows personal/induvidual edition is absolutely not private in the sense your data is yours and not leaking to M$. That should be abundantly clear when they now are now deeply integrating ChatGPT, and it's just another step in their road of showing you more and better ads based on what you do in their OS.
Don't forget they have for many years sniffed on the idea of giving Windows away for free, and they are already doing it for tons for ppl with free major upgrades.