There's a Windows app for iCloud that integrates keychain into Edge. It's what I use when I'm on Windows.
As krakenrelease says it's not a perfect UX but it works fine. The only inconvenience is I have to type a PIN in to unlock it most times I go to use it (probably because I don't use it often). The PIN shows up in the bottom right of the screen so it's very easy to type in, it just feels weird copying a number from one part of the screen to another - makes you think "why isn't this just done automatically behind the scenes?". Probably some technical security reason.
So yeah, it's slightly clunky, but entirely usable. I wouldn't use it if I was mostly Windows based, but that goes without saying really doesn't it - why would you use the Apple solution if you weren't predominantly Apple-based. For the odd times I need it on Windows it's fine.
A hacker would need access to both your iCloud password, and one of your authenticated devices. You're outside the realms of what an ordinary person has to worry about there - that's a hardcore, targeted attack with physical intrusion. If you're at risk of that then you need some serious security, not consumer grade stuff.