I'm not saying it's impossible, because theoretically unless you block out all outgoing/incoming requests to windows servers, which can include updates, telemetry data, and all sorts of data you agree to submit by default, then Windows can have access to your data.

This is even possible for linux/ubuntu because software and package updates are enabled by defaukt, but since its an open source OS, updates are coming from a public repo, its hard to wear a tinfoil hat that big and believe that all Arch devs are out there to take your bitcoins

But even for Windows, dont you think its a bit too far? If you were to mistrust big corporations, the damage they can do to you if they go "rogue" is laughably dangerous. Do you use Gmail? What if Google filtered all emails related to blockchain, web wallets, and private keys? You trust google? So what about your ISP? Maybe they could intentionally modify your traffic to screw with your payments... You can clearly see I can go all day with this, from your laptop down down to your smart toaster connected to the internet, if you were to distrust everything around you, youd never sleep.

But maybe it can help you to think of how relevant of a target you are. Do you really think Windows or any other entity that you unwillingly have to trust, care about targetting you specifically? You know there are probably hundreds or thousands of people richer than you that use that operating system, chances are very unlikely that youd be targetted unless a massive breach happens within these corporations.

On another note, just make sure your windows is legit. Ive seen with my own eyes pirated windows copies that run a miner process upon installation.