If you are using archlinux, you can install from pulxc-git in AUR
But you still need to configure sysctl and lxc-usernet
kernel.unprivileged_userns_clone=1
#/etc/lxc/lxc-usernet
pulxc veth pulxcbr0 99 255
useradd -b /var/lib -m -r pulxc
touch /etc/subuid
touch /etc/subgid
usermod -v 100000-165535 -w 100000-165535 pulxc
use the tool you want
#/etc/systemd/network/pulxcbr0.netdev
[NetDev]
Name=pulxcbr0
Kind=bridge
#/etc/systemd/network/pulxcbr0.network
[Match]
Name=pulxcbr0
[Network]
Address=192.168.100.254/24
configure ip forwarding and NAT if you need it.
you can modify the uid/gid/subuid/subgid in Makefile to meet your pulxc's uid/gid/subuid/subgid
make
make install