My intention is not to move a save file to a PC to for the intent of playing it there, I merely want to back it up, but I can't seem to find a way how to: not with an Android file explorer or moving the file to a PC, I tested it and it also happens on N&F
The game engine we use, Renpy, may not be compatible with the Android file explorer. The compiled Android builds aren't really workable with the PC even if you're just trying to backup files. I'm sorry I don't know a solution to this.