Kirk McElhearn and Joshua Long writing at Intego’s Mac Security blog:
Apple released iOS 15 and iPadOS 15 on Monday, September 20, and, as usual, many people updated their iPhones, iPads, and iPod touches to the new operating systems. But unlike in the past, Apple is not pushing people to make the upgrade. For the first time, Apple is going to maintain the previous operating system for users who don’t want to upgrade. You can choose to remain on iOS 14, and still get essential security updates, if you’d rather not move to iOS 15. (When I mention iOS in this article, I also include iPadOS.) This is similar to the way Apple manages macOS; you can upgrade to the new version, or continue to receive security updates on the previous version.
When Apple announced it would be creating two update tracks, I assumed that minor updates to the existing operating system would be listed in the “Also Available” section. But it turns out that is not the case: new versions of iOS 14 are given top billing in the software update screen, and iOS 15 is in the secondary area, kind of like Apple is shy about its availability. This is a much quieter notification than in years’ past.