Off-Centred Fullscreen

[DiDDiT]

I can't find any fixes for this issue and I don't know where else to put it, but I'm out of options. I'm trying to start up Pixelmon Generations so I can play it with my friend, but no matter what I do, the fullscreen is ALWAYS off-centre. I've tried changing the in-game resolution, the launcher resolution, changing different graphics settings, the GUI scale, turning stencil buffer on and off, I just can't find any fix whatsoever. I'm on a 4k monitor which I think is the core of the issue, and this issue is really making me mad. The centre is usually to the right of my screen. I have a geforce rtx 2070 8gb.