Following up on my comment in the other thread (A highly-amateur census of hardware-accelerated video decoding issues: - #4 by Aidan), it may be worth trying the Firefox flatpak (version 110) on Zorin. I have never gotten hardware decoding to work with snap Firefox, and vanilla Ubuntu installs the snap version by default - annoyingly, even if you use “apt” to install it. Zorin OS may do this also.
I think the only thing you need to do to enable HW decode on flatpak Firefox is to set “media.ffmpeg.vaapi.enabled = true” under about:config. My understanding is that it just uses the runtimes that are packaged with flatpak (“org.freedesktop.Platform.VAAPI.Intel”) to do the HW acceleration.