This is probably the best instructions I have seen for any debian/ubuntu-like LXC guest to run the docker engine. Works with proxmox 7.2x and definitely Ubuntu 22.04, other ubuntus reasonably sure - and I believe with Debian10-11 as well.

Take care to go to the docker docs for the exact installation lines since they are a little different by now than what's written here - the author takes care to mention it as well.