The EOL was your issue. On this site the notice is here (warning posted 1-June-2022, wording slightly altered though post-EOL on 16-July-2022)
Lubuntu’s official blog notice is here
A Ubuntu warning notice of EOL (~six weeks before EOL) can be seen here - Ubuntu Fridge | Ubuntu 21.10 (Impish Indri) reaches End of Life on July 14 2022
with an EOL notice here - Ubuntu Fridge | Ubuntu 21.10 (Impish Indri) End of Life reached on July 14 2022 though that’s only a single example, posted by Ubuntu News which propagates to a number of sites, itself a formatted copy of the ML notice.
A quick way to calculate the EOL of a release is
(1) when is it released; in this case it’s 19.10 meaning the 2019-October release.
(2) it’s not an LTS release as it’s not the first release of an even year, thus it’s support is 9 months. For LTS releases it’s 3 years if a flavor like Lubuntu, or 5 years for Ubuntu Desktop/Server/Core/Cloud.
2019 October + 9 months = 2017 July for EOL.
Even without remembering (or looking up the release notes to get day of month), as releases are usually the 2nd, or 3rd Thursday of the month, so looking at a calendar without knowing, would mean you’d guess the 14th (2nd Thurs of July 2022) or 21st of July 2022 (3rd Thurs) for EOL/end-of-life. This quick calculation is usually at most a week out (ie. if you guessed 3rd Thursday you were a week off. Also note if there are 5 Thursdays in that month the release may also be the 4th)… The year.month format of releases makes it pretty easy.