Switching rootless Docker to lxc-user-nic network

Not sure if this is the right place for this, so Admin’s feel free to move.

Am experimenting with rootless Docker, via a Compose project, and am trying to find documentation of how to switch it entirely to using lxc-user-nic networking for the rather drastic speed gains. Out of the box it’s running slirp4netns with associated options and it’s slow.

Having added the necessary file at etc/lxc/lxc-usernet, and added Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_NET=lxc-user-nic" to my override.conf. Restarting Docker, ps -x shows it attempting to start up with lxc-user-nic networking, but then it craps out entire and running any Docker command says it can’t access the socket.

What else do I need to do? Documentation seems to be slim on the ground, even on this forum. Do I actually need to set up an lxc network outside Docker first? Is there a full list of things that can be entered into the override.conf?

System specs:
Ubuntu 22.04 LTS
Docker 20.10.22