It's in Ubuntu's Universe repository. That means it's usually just the upstream Debian package or one maintained by the community rather than Ubuntu itself.

Ubuntu's podman 3.4 was pulled from Debian Unstable at some point (Debian Stable is still on 3.0?). It looks like Debian Testing has 4.3, so they're probably waiting to just use that from Debian Stable in Ubuntu Lunar rather than the community maintaining their own version.

https://code.launchpad.net/ubuntu/+source/libpod