I get lots of weird texture glitches when outdoors, had it for at least 3 versions with different PCs so i doubt it's GPU issue but haven't seen anyone else complaining about that
Both GPUs were AMD tho
Though, I don't know the exact reason for this weird flicker on open maps, I suppose, it's something to do with how different renderers do illumination or global shading. I, too, had this problem on my RX580 GPU. Probably, it just doesn't support some new rendering features. In other words, it's probably rendering mode issue.
That said, I've stumbled upon a way to fix this. You can run the game in DX12 mode, which eliminates (so far, on my PC) all the flickering.
Just unpack the attached Yuna DX-12.bat (inside the archive) into the game directory, where Yuna.exe is located. Run the game via bat file and it will launch in alternative rendering mode. Since the directory structure is the same for different versions it might be working for both older or newer versions of the game as well.