@VisionSubsea could you test this version of Cockpit in the machine you were using. I have added some things on it to generate data for us around the GPU usage.
If you can, open it, right click the video player widgets and enable “stats for nerds” in their configuration dialogs, and take a screenshot of it for both video streams.
Also, go to /menu/settings/dev and use the “copy” button in the system information section to copy the data and paste here.
My goal is to see if you’re system is using the hardware video acceleration.