The command to set the group for the multi-user daemon is:
sudo snap set lxd daemon.user.group=<user_group>
It looks like you may have initially set this to users and then set it again to admin, which the current user is not a member of.
You can find more information here: https://documentation.ubuntu.com/lxd/en/latest/howto/projects_confine/#confine-users-to-specific-lxd-projects-via-unix-socket