Extremely slow when used with external monitors

I’ve recently upgraded my setup, and I’m using a Dell Latitude 7320 docked to a WB19TB docking station (via a thunderbolt 4 port) , which has 2 external monitors connected via DisplayPort.

Qubes works as expected on the laptop, but its performance is abysmal when the external displays are connected. I’ve been experiencing terrible lags, and dom0’s cpu usage (as reported by xentop) constantly balloons to well over 100%. The system slows to a crawl when videos are played, rendering it completely unusable. I have a video showcasing the issue, but I’m not allowed to upload it (new users cannot upload attachments).

I’ve tried experimenting with xorg configurations, updating to the latest kernel, etc, to no avail.

Would anyone be able to assist?

You have neglected to say what the external monitors are, and what
resolution you are using on them.
Does this happen with any video? Is the effect mitigated if you
reduce the size of the video window?
Do other applications perform as normal? (Terminal windows, office
apps, etc.)
What are the “terrible lags”? You instance video. What about (e.g.)
mouse movement, key press?

I never presume to speak for the Qubes team. When I comment in the Forum or in the mailing lists I speak for myself.

I’m using 2 Dell QHD monitors (P2423D), which are connected to a WB19TB dock, which is in turn connected to one of my laptop’s thunderbolt 4 ports. I’m able to use both of the displays at 1440p on Qubes.

Dom0’s cpu usage constantly spikes to well over 100% at times, and terrible performance can be observed. There’s noticeable lag when moving windows around, with mouse movements, scrolling, keyboard input takes a while to show up, etc, which applies to all of the applications, including the ones in dom0.

It happens with any video, probably because the system already lags like hell. Reducing the video quality and window size does not appear to mitigate the issue.

I’ve uploaded a video showcasing the issue. Do note that it leads to an external link as I’m unable to upload mp4 files as attachments here.

When I’m using my laptop on its own, none of the issues are present.