A page of Ubuntu releases, when they were released, and when they will no longer be supported.
RSS: https://wiki.ubuntu.com/Releases?diffs=1&show_att=1&action=rss_rc&unique=0&page=Releases&ddiffs=1
endoflife.date is a community-maintained project to document end-of-life dates, and support lifecycles of various products.
Github: https://github.com/endoflife-date/endoflife.date
API documentation: https://endoflife.date/docs/api