For example, Spotlight, ever since their updates, is now unable to find any of my applications, struggles to find PDF documents while being slower and worse than the spotlight I used to use in OS X Snow Leopard. Yes, my current Mac's spotlight has more features. But the core functionality no longer "just works."
Another example is networking. For some reason, MacOS is now really flaky when using VPNs and it seems to have struggle connecting with WiFi networks from time to time. It's bizarre.
I'm using the latest hardware (the 28GB M2 MacBook Air) — it shouldn't be this bad.
Let's not even talk about Apple Care. Apple Care theoretically does more now, but they've made it functionally worse for most consumers.