Is 4k @ 120hz possible with the USB4 on p14s gen 4?

[Relevant PSREF](https://psref.lenovo.com/Product/ThinkPad/ThinkPad_P14s_Gen_4_AMD)

I've been loving the p14s the past few weeks, but there is one nagging problem I can't find a solution for. I have both a 4k and 3800x1600 monitor, and the best refresh rate I can seem to get is 75hz at 3800x1600. The PSREF states that it can only support 4k @ 60hz, but given that this laptop supports HDMI 2.1 and USB4, it seemed like there had to be a workaround. HDMI was a no-go, so I tried a USB4 to HDMI cable (CableMatters) in the USB4, but I was still stuck at 75hz. I pulled out the failsafe and hooked my eGPU (Razer Chroma) to the USB4 port. HDMI to my eGPU still resulted in 75hz, so I tried displayport between the monitor and the eGPU, but my monitor wasn't detected. I've used both approaches before with other USB4 laptops with success.

At this point I'm not sure if there is some technical limitation with the 7840u that makes this impossible or if Lenovo's implementation of USB4 for this laptop is incomplete. Does anyone have any suggestions or know if this is at all possible?