I had the exact same setup as the original poster, namely Ubuntu 22.04 on ARM in the Oracle Cloud with default networking setup by lxd init and at least got this running now.
First i followed the advice from the official documentation [0]
sudo ufw allow OpenSSH #don't brick yourself
sudo ufw enable
sudo ufw allow in on lxdbr0
sudo ufw route allow in on lxdbr0
sudo ufw route allow out on lxdbr0
but it still didn’t made any noticeable difference. Then (me obviously being a noob) i got the idea to inspect the systemlog
sudo journalctl -r | less
and found error messages from apparmor, relating to lxd, some of them like this:
Feb 27 02:32:32 vmporto4 audit[2778]: AVC apparmor="DENIED" operation="capable" profile="snap.lxd.lxc" pid=2778 comm="lxc" capability=2 capname="dac_read_search"
I wasn’t able to resolve that, so as a start i simply disabled apparmor [1] for now and rebooted, that worked:
sudo systemctl disable apparmor.service
sudo reboot
[0] https://linuxcontainers.org/lxd/docs/master/howto/network_bridge_firewalld/#ufw-add-rules-for-the-bridge
[1] https://ubuntu.com/server/docs/security-apparmor