Use proxy type for X0 device, the profile I am using:
lxc profile create x11app <<EOF
config:
environment.DISPLAY: :1
description: Default LXD profile
devices:
X1:
bind: container
connect: unix:@/tmp/.X11-unix/X1
listen: unix:@/tmp/.X11-unix/X1
type: proxy
eth0:
name: eth0
network: lxdbr0
type: nic
root:
path: /
pool: default
type: disk
EOF