Seems the latest version in the ubuntu repos haven't been updated for a while. Latest version is 3.1.2:

$ apt policy podman
podman:
Installed: 100:3.1.2-1
Candidate: 100:3.1.2-1
Version table:
*** 100:3.1.2-1 500
        500 https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/xUbuntu_20.10 Packages
        100 /var/lib/dpkg/status
     2.0.6+dfsg1-1ubuntu1.2 500
        500 http://us.archive.ubuntu.com/ubuntu groovy-updates/universe amd64 Packages
     2.0.6+dfsg1-1ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu groovy/universe amd64 Packages

Is there any reason for not updating them? Looks at the repos this is the case also for Debian 10 (3.0.1) and Ubuntu 21.04 (also 3.1.2).