SOLUTION: Idk if I just didn't have the DisplayPort cable pushed in far enough for what. Swapped DisplayPort outputs on the back of the GPU and that seemed to have fixed it.
So I finally got around try playing some games with my new RTX 3090 FE and get greeted by this instead. Is this card like, too powerful for my monitor to handle? Originally I was thinking it might just be a power supply issue as I only have a 750W 80+ Gold unit from EVGA, but I have a UPS that supports up to 1000W of power and the built-in screen says my system and monitor combined draw like 580W of power.
GPU is plugged into the DisplayPort connector on the back, and the monitor is the LG 34UC87C. I was planning on upgrading to a 144Hz panel anyway, but wanted to wait until after the holiday season if possible so I could recover from the burnt hole in my pocket left by my RTX 3090 purchase haha.