I' still seeing an error in console when I launch Firefox in a Wayland session
nVidia GPU

I verified that the kernel loaded with nvidia-drm.modeset=1

cat /proc/cmdline
initrd=\EFI\com.solus-project\initrd-com.solus-project.current.6.2.14-232 root=PARTUUID=a7a26d35-2150-7f48-9225-78b81a6f62ea quiet loglevel=3 splash systemd.show_status=false rw radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1 nvidia-drm.modeset=1

nvidia-vaapi-driver is installed.
Installed package:
Name : nvidia-vaapi-driver, version: 0.0.9, release: 11

In about:support I see "Compositing WebRender" (it does not show "software") so hardware rendering is enabled
In about:config

gfx.webrender.software is false
media.ffmpeg.vaapi.enabled is true

NVD_BACKEND=direct MOZ_DISABLE_RDD_SANDBOX=1 env variables are set

❯ echo $NVD_BACKEND && echo $MOZ_DISABLE_RDD_SANDBOX
direct
1

When I start firefox in Wayland from console I still see this:

[GFX1-]: glxtest: VA-API test failed: failed to initialise VAAPI connection.
[GFX1-]: Wayland protocol error: warning: queue 7fac1c0feaf0 destroyed while proxies still attached:

[GFX1-]: Wayland protocol error:   wl_registry@64 still attached

So, to be clear, have you also activated the additional options mentioned here: https://github.com/elFarto/nvidia-vaapi-driver#firefox ?

So in about:config
widget.dmabuf.force-enabled true
gfx.x11-egl.force-enabled true (or env MOZ_X11_EGL=1)

and env variables

EGL_PLATFORM=wayland
plus maybe LIBVA_DRIVER_NAME=nvidia (since you have dual-gpu, even though this option should no longer be required.