Ubuntu and all flavors of Ubuntu release at the same exact time, with the authority of the release overall managed by the Ubuntu Release Team.
Yes they consult with us (via IRC & other means), and prompt us to mark a product ready on-time or early (see http://iso.qa.ubuntu.com/qatracker/milestones/432/builds on the ISO QA tracker (where you’ll note all were marked as READY; except for Ubuntu WSL), so that everyone can release at the same exact time (or special notices go out, including delays)
Not all postings for a release occur at the same second, as the Ubuntu Release Team have a set of procedures they follow, and this takes a number of hours once the ‘go’ has been achieved, and so many release announcements occur over a number of hours. An example maybe the Ubuntu Fridge post I quoted from in my first reply, the text of that I get from the Ubuntu Release Team’s Mailing List notice, so I can’t start putting that together until the ML post has gone out (very late in the release process), and Fridge posting requirements mandate another Editor validate what I did, which again takes time etc. ( Note: I’m using that example; I do that as part of my Ubuntu News duties, unrelated to Lubuntu; Ubuntu is a family; Lubuntu being one part)
Upgrades from Lubuntu 21.10 to Lubuntu 22.04 LTS, or in fact from Lubuntu 20.04 LTS to Lubuntu 22.04 LTS are not unique, in fact the Ubuntu Release Team handle those being available as well given all flavors (including Lubuntu) use the same ubuntu-release-upgrader tool, with the Ubuntu Release Team controlled the meta files that control what releases your system sees (ie. meta and meta-development).
In the end it’s identical for all Ubuntu, and flavors of Ubuntu. Lubuntu do not provide release schedules as you may have noted in the Lubuntu jammy jellyfish issue tracker where we only provided Ubuntu links, as we use those same alpha, beta, freeze, RC etc dates.
One difference is support for LTS releases. Packages provided on Ubuntu ISOs have five years of support, where flavor ISOs (like Lubuntu) and packages from the ‘universe’ repository, come with a shorter life span (3 years for packages included on LTS ISOs).