Expanded Security Maintenance for Ubuntu’s Main repository for an additional 5 years beyond Ubuntu LTS end of standard support (infra-only)
Coverage levels
Infra-only coverage
Encompasses over 4,700 open source deb packages in Ubuntu’s Main repository for an additional 5 years [...]
Full-stack coverage
Provides security maintenance for over 36,000 open source deb packages in the Ubuntu Universe repository for up to 10 years, including [...]
TLDR: They withhold Ubuntu patches in the Universe repo without Ubuntu Pro.
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If Canonical creates a security patch for a universe package, that patch is gated behind Ubuntu Pro. Standard systems will display notification prompts that security updates are available via Ubuntu Pro, but running sudo apt upgrade without Pro enabled will skip them.
Look at the descriptions
https://ubuntu.com/pricing/pro
Ubuntu Pro:
Expanded Security Maintenance for Ubuntu’s Main repository for an additional 5 years beyond Ubuntu LTS end of standard support (infra-only)
Coverage levels Infra-only coverage Encompasses over 4,700 open source deb packages in Ubuntu’s Main repository for an additional 5 years [...]
Full-stack coverage Provides security maintenance for over 36,000 open source deb packages in the Ubuntu Universe repository for up to 10 years, including [...]
TLDR: They withhold Ubuntu patches in the Universe repo without Ubuntu Pro.
---
If Canonical creates a security patch for a universe package, that patch is gated behind Ubuntu Pro. Standard systems will display notification prompts that security updates are available via Ubuntu Pro, but running sudo apt upgrade without Pro enabled will skip them.