I'm also getting the "a newer version of the game has saved this level" and am using the Windows 10 version. The world in question had been used as my realm, but I recently switched the realm to a different world, and now I can't open the original.
I made a backup copy and tried using the Universal Minecraft Editor to do a fix I found by Googling, but the result is the same. Is there any way I can get this world back? I have been streaming it weekly for several months now, really hate to lose it. (Yes, I should've backed it up, thought I had, but apparently not.)
The hotfix did the trick! It's back up, all items seem to be intact... and yes, I IMMEDIATELY made a backup. LOL
Thank you! 🙂