So the weird thing here is that NVIDIA contributed both the LXC and Docker integrations.
But they made it so that the LXC integration only works with unprivileged containers whereas the Docker integration only works with privileged containers, so that’s how we end up with this weird mess.
The only workaround I’m aware of is to not use nvidia.runtime on the Incus side but instead go through the annoying process of installing all the NVIDIA packages directly in the Incus container, at which point, that container can be privileged and the Docker support should work as expected.