I really enjoy Linux but I find myself having to keep Windows partitions around for software that specifically requires Windows.
Proton makes everything easier by automatically running game files through a translation layer, and it “just works” quite well most of the time.
Also VanillaOS can apparently auto-spin a container when you try to open a .deb or AUR package (this is my rudimentary understanding).
Setting up WINE/Bottles, etc. is above my pay grade.
Is it not possible to create an OS that just does the same thing as Steam but for the entire OS?
Zorin already does that out-of-the-box. See: https://help.zorin.com/docs/apps-games/windows-app-support/#run-apps-in-exe-and-msi-files
And if you want to take it to the next level, there’s ReactOS, which is basically an opensource reverse-engineered Windows - but sadly it’s development is slow and it’s hardware support is extremely lacking. But it exists, and does qualify as an answer to your question. For all practical purposes though, Zorin is what you’re looking for.