just a quick snippet. if you use active directory and join unprivileged containers to it then you need to make sure that proxmox supports the uid/gid that ad will give the user when using sssd.
i didn’t really see much documentation for this but the format for /etc/subuid and /etc/subgid would look like this:
root:400000:9999999999
just a quick… root:(first uid/gid):(number of uids/gids after first)
you also have to do some mapping tomfoolery in the (lxcid).conf in /etc/pve/lxc … but this one had me stuck for a minute because i wasn’t quite sure how the numbering worked.