just supports include directives under the --unstable flag which is enabled by default with a shell alias set in /etc/profile.d/. If you have a posix-incompatible shell such as fish, you will need to alias just to just --unstable manually or wait until just PR #1588 merges, and you’re able to set it as an environment variable instead.
sudo v4l2loopback-ctl set-caps h264 1920x1080@30waydroid, but i'd need to figure out wayland nested desktop inside X11 for that to worksudo v4l2loopback-ctl set-caps h264 1920x1080@30waydroid