People have been saying that since OS X first came out, and OS 9 was so buggy it had a famous cute bomb icon for when it crashed.

I'm using MacOs/OsX since Lion, and I can say that it was very stable (even on my Hackintosh) and I observed stability issues increasing with all the following versions (on real Apple HW) and I'm on the same ship as GP never upgrading to newer versions until at least 6 months pass.

Yeah, first few OS X releases were famously buggy as they were figuring this UNIX stuff and the OS 9 compatibility, but they stabilized about 10.4 Tiger.

Honestly the OS X itself (uhhh macOS now) is still fine, even with Big Sur and its weird iOS controls, however the other software is sometimes weird; but - let's say Numbers was never good and iWeb was always downright bad. And iTunes was bad in Jobs era and is still bad (as Music).

I however still kind of miss when native Cocoa apps were sort of good and not just ported iOS app via Catalyst or something. But whatever. I'm old I guess

Don't the bomb icon and "Sad Mac" go back to the very beginning?

When OS X came out 20 years ago, it was the star of the show. Nowadays it's just an annoyance that Apple has to keep around. The quality has demonstrably fallen, and the internal struggles it's had within Apple have already been documented.

Honestly, Apple's decline traces back to losing Steve Jobs. The strategic changes were immediate, (and aimed at shorter term gains, things that people besides Jobs thought were being left on the table) the effects just took a long time to really add up to something meaningful. IMO, they never really recovered, they just are massive and have a HELL of a lot of momentum. It takes time to undermine that all even if you do everything wrong. They definitely are still doing some things right, but IMO, the type of thing you are complaining about is a leadership issue.