Ubuntu used to have security support for "main" only. All other software, e.g. in "universe" had patches trickle in from debian but no dedicated support. This is particularly problematic for long or extended LTS when debian has dropped the old stable release that would be pulling from.
"Ubuntu pro" is basically trying to fix this shortcoming compared to debian and to pay for a security team for universe. It is available as a subscription.
TLDR: If you use software from main it is completely irrelevant. If you use stuff from universe it is now as good as debian, if you pay (first 5 devices are free).
