Dropping this here in case anyone else runs across this post like I did.
I recently upgraded to Proxmox 7 and my ZeroTier stopped working. During the upgrade, I had a warning about cgroup which I had forgotten until now was the magic ticket for LXC + ZeroTier. On Proxmox 7, it looks like this is now `cgroup2’ so the above config changes work perfectly if you make that swap.
Example:
cgroup changes to cgroup2
lxc.cgroup2.devices.allow = c 10:200 rwm
lxc.hook.autodev = sh -c "modprobe tun; cd ${LXC_ROOTFS_MOUNT}/dev; mkdir net; mknod net/tun c 10 200; chmod 0666 net/tun"