Is it possible to copy saves, states, thumbnails, etc between Windows 10 and iOS RetroArch? Do you need software on a PC, besides iTunes to access the RetroArch folder on iOS? If so, do you recommend any free software?
I don’t know of any way for iOS, no.
Yes, but save states may not work if using different versions of a core. As long as the retroArch folder shows up in iTunes, you should be good. I transfer files using iCloud, but DropBox, Goole Drive, etc. will also work. You can get to the RetroArch folder using the Files app on your iOS device. It will be under On My iPhone/iPad.
Should be able to as already said as you use the Same Cores then it Should Work.
Don’t think what OS you are using