https://github.com/conjure-up/conjure-up/issues/1440
It seems like the the installation is complaining because it needs an "IPv4-only" network, not just any network or no IPv6 at all. Installing kubernetes I faced the same issue. Disabling IPv6 in the lxd network solved the issue for me. Like this:
lxc network set lxdbr0 ipv6.address none