It seems that in the "earlier" versions of a new Mac OS, such beta releases happen faster. But as the OS matures, they come later, and eventually stop.
According to
MacTracker Sierra, High Sierra, Mojave, and Catalina were launched in late September and early October with updates the last of October, early December, late January, late March, May, and July, Catalina had an additional release in September, probably due to the delayed launch of Big Sur pending the availability of Apple Silicon Macs. So, it would seem, Big Sur is pretty much on schedule If you factor in its late launch. The subsequent version in each case was previewed at the World Wide Developers Conference in Early to mid June and beta tests were in full swing before the July update and most of the beta testers and the bulk of the OS development team had transitioned to the upcoming version. I will not be surprised if are were only five MacOS 11 updates, assuming MacOS 12 makes the normal last week of October, first week of September launch date.
So in essence your adoption decision is driven by the calendar and Apple's carefully orchestrated development/support schedule.
From what I remember:
1. Moved to High Sierra in November 2017.
2. Moved to Mojave in December 2018.
3. Moved to Catalina in January 2020.
Each of those were driven by the compatibility of Tech Tool Pro. And as I have said many times, the time when I finally move to the latest version of the new Mac OS is when all my third party applications are compatible. It just so happens that Tech Tool Pro has always been the last one.
For Big Sur, I am still anticipating sometime in the latter part of January, or possibly February. The "theory" is that SuperDuper! will release a compatible version soon (looks like sometime in January), and Tech Tool Pro will follow thereafter.
Also, although both High Sierra and Mojave were initially released in September (2017 for High Sierra, and 2018 for Mojave), Catalina was not initially released until October 2019, and of course it was November 2020 for Big Sur.
As for Catalina, the May, OS 10.15.5, release was the one that caused issues for SuperDuper! and Carbon Copy Cloner. I'm of the opinion that is the primary reason for the release that came out in July, OS 10.5.6. So possibly there may have only been OS 10.15.5 (was OS 10.15.6). But not 100% sure about that.
