[xdanger]

I did something similar for my macbook with uxplay: https://github.com/FDH2/UxPlay

I ran it in console directly rendering to framebuffer and it has hardware-accelerated video decoding. On Raspberry pi 3, hooked to lan and my macbook on wifi the lag is ok. It's about the same as ssh over slow cellular. I mainly run my terminals watching the logs/builds etc. on that display.

[xdanger]

Just to let people know how to get the latency down with uxplay:

    Upgrade the debian to bookworm (uxplay is in the repos for that one)
    apt install uxplay
    
    in in /boot/config.txt
    change doverlay to:
    dtoverlay=vc4-kms-v3d
    force hdmi: (i had some problems with kms)
    hdmi_force_hotplug=1
    add gpu mem:
    gpu_mem=256

    then run: (-a disables audio)
    uxplay -vs kmssink -a

and now you have and airplay monitor that can mirror or extend your desktop.

[pcouy]

The hard part for me was getting the latency low enough that I can comfortably type and move the mouse. But I may look into is as a 4th screen for logs would be interesting