Weird pillarboxing when playing games

[Thaidos]

Hey so I recently upgraded my 1440p monitor to the 4k 144 hz LG GN950 and since then I've been getting this weird kinda pillar box effect in some games. Mafia 2 does it in borderless windowed mode, but once I switch it to full-screen it works like normal. Phasmophobia doesn't work at all and I can't figure out a fix. I've tried restarting, updating the GPU driver and DDU'ing it, looking for a config file (there is none), forcing windowed and full-screen through Steam, using Borderless Gaming on it, changing the desktop resolution, nothing works. I could use some help if anyone has seen this behavior before or has any clue what's going on. Attached are screenshots of Mafia 2 and Phasmophobia respectively in this state. Thanks in advance!

 

Specs in case you need it:

Intel i7 8700k

RTX 2080 Founders

32 GB Corsair 3200 Mghz RAM

GPU Driver version 456.55

 

Mafia 2:

Phasmophobia:

 

edit: I did some quick math an measurements and it looks like it's running at around 384 x 2160, like it missed a 0 somewhere along the line, not sure if this helps, but it's interesting