[update Feb 2021] A new release of a TurnKey LXC appliance has been deferred until v17.0. Hopefully with the newer versions of LXC and systemd it will "just work".
I have been working on the v16.0 release of TurnKey LXC and due to issues with running privileged Debian Buster containers on a Debian Buster host we need to significantly refactor it. I've personally spent a ton of time on it and whilst I've had some progress, I've yet to get unprivileged v16.x containers running on a v16.x LXC host.
So I'm deferring the v16.0 release of LXC for now...