Windows 10 because I can't upgrade to 11 for some arbitrary reason. I tried Ubuntu years ago but it was so much work trying to get it to just work that it really put me off. So unless the Linux ecosystem improved and by a wide margin and it has decent support for the software I use, I don't think I'm changing anytime soon.
In the last 2 years a lot has happened. I suggest you try PopOS or Fedora. I switched from Windows to PopOS 2 years ago on my main PC. There is a learning curve but if you want to know how something works a search of "how to do thing PopOS" or "how to do thing Ubuntu" gives quick results. PopOS is similar to Ubuntu in many ways but way nicer in others.