Changing to a yearly release cycle is what made quality and stability a non-priority. MacOS has been buggier and buggier since
In my opinion, the drop in quality was probably at least also related to Steve Jobs‘ death.
That's not correct. Here are the # of months since the previous Mac .0 release:
10.1.0 6
10.2.0 11
10.3.0 14
10.4.0 18
10.5.0 30 (delayed due to iPhone)
10.6.0 22
10.7.0 23
(Steve Jobs resigns)
10.8.0 12
10.9.0 15
10.10.0 12
10.11.0 11
10.12.0 12
10.13.0 12
10.14.0 12
10.15.0 12
This was a logical progression until 10.8. The fundamental software development principle is that immature software is easier to improve, because there's a lot of low-hanging fruit — glaring bugs and missing features — whereas mature software is harder to improve and easier to accidentally break. That's why major updates should come more slowly as the software matures over time.
It's no coincidence that Tiger and Snow Leopard are viewed as high points in Mac OS X quality and stability. It's not because of the .0 releases, which were very buggy like any .0 releases; it was because they ultimately became very stable after many many months of minor bug fix updates with no major updates (30 and 23 months respectively).
Also worth mentioning: major Mac OS X updates used to cost $129. Now they cost $0. You get what you pay for. Now users are pushed into updating whether they like it or not. You might wonder whether the principle starts to apply: if you're not the customer, you're the product. After all, Apple has been transitioning into a so-called "services" company. They'd rather sell yearly "subscriptions" (more accurately, rentals) than major OS updates.
> In my opinion, the drop in quality was probably at least also related to Steve Jobs‘ death.
This may be true, but note that the change in OS release schedule coincides with the death of Jobs. Mac OS X 10.8 was the first post-Jobs release and also the start of the annual schedule.
There's no such thing as a major bugfix release. Every major update introduces more bugs than it fixes, and Sonoma is no exception to that hard rule. Which bugs were fixed? I've personally filed multiple new bugs against Sonoma.
I wrote about this in my previous comment: "It's not because of the .0 releases, which were very buggy like any .0 releases"
MacOS has had to keep up with a relentless march in services and devices each with their own peculiarities.
iPhone has had to have an annual release cycle, and there are multiplatform apps and crossplatform features to maintain and extend on deadline.
I can certainly see that if the emphasis on new features greatly outweighs that of bug fixes and improvements, then you can extend the implementation months for larger features because you can just bleed the bug fixes and improvements into next year's release. But then that year's feature set takes precedence and dept accumulation occurs.
My own experience with macOS is that it stopped "just working" a decade ago Apple stopped caring about it and poured everything into iOS. And then this is exacerbated by today's mode of operating by just treating features like they're free and frequent release cycles.
A regular release cycle that focuses on security, stability and incremental improvements, is fine as long as there isn't a need to constantly push new features in.