In theory you should be able to do that! I think Proton has some issues with NTFS, mostly when installing or updating, but with a little research and tweaking you should be able to get it to run smoothly. I opted to keep them fully separate and just installed certain games twice, but am also using this as a test run before diving into full daily driver Linux when I build a new system in the spring, so longevity of my storage drives wasn’t a concern.