Ubuntu Pro is a subscription offering for Ubuntu users who want to pay for the assurance of getting quick and high-quality security updates for Ubuntu. I tested it out to see how it works in practice, and to evaluate how well it works as a commercial open source service model for Linux.\n
Huh, that was hidden deeper than I like. https://ubuntu.com/security/cves/about#security
https://help.ubuntu.com/community/Repositories/Ubuntu
https://askubuntu.com/questions/1452497/what-are-esm-apps-and-how-do-they-relate-to-ubuntu-pro
edit: adding some relevant links
From the link:
I’m not sure every package should be considered supported in LTS, so this not being available by default looks ok for me