Im trying to run a mod for Skyrim called the Unofficial Downgrade Patcher. I can get it to open by using proton tricks. But the folders are not showing up for me to input the game. I have winecfg set to show dot files so I don’t know whats going on there. Besides that some one on reddit said I can paste the file path but it needs to be windows format. So my question is how do I make a Unix file path to a windows file path?
Welcome to the forum! 
If you’re trying to browse your file system from the Windows program, you’ll see your regular file system mounted under drive Z: or /. From there, just browse to your Steam directory where _SkyrimSELauncher.exe (assuming you have the Steam Special Edition installed) resides. That would normally be /home/Vivid/.local/share/Steam/steamapps/common/Skyrim Special Edition/