Red Hat
The blog post from Red Hat is similar to posts from other operating system providers. Red Hat is selling extended support contracts for Red Hat Enterprise Linux 7. They are meeting a business need for the customers that purchase their products.
Canonical
Canonical offers something similar for subscription users that are running Ubuntu 18.04. They describe their Ubuntu Pro product and its Extended Security Maintenance in their March 2023 blog post.
Microsoft
Microsoft offered something similar for subscription users running Windows 7 after its end of support in January 2020. They announced it in the post on their learning site in 2020:
Summary
The Jenkins project has not extended its Linux support policy or its Windows support policy beyond the public end of life for any of those operating systems. It does not seem reasonable to me that Jenkins as an open source project supporting publicly available operating systems would purchase extended operating system support from the operating system providers.
I’m open to disagreement from others in case they feel that there is some path where an operating system that has reached its public end of life should continue to be supported by the Jenkins project after the public end of life.