For as long as I can remember on macOS, keyboard layout switching has never worked properly for me, and I've been on good terms with Macs since the Snow Leopard days, probably. I'm talking about the most default behavior of a Mac straight out of the box.
So, problem number one - language switching on Caps Lock, which you can set with just a checkbox in system preferences, somewhere in one of 5-10 cases is simply ignored. That is, I pressed the button, felt it tactilely, but the language didn't switch. Insanely frustrating. Someone suggested I could install Karabiner, remap Caps Lock to F13 for example, disable Caps Lock switching in settings, and set switching to F13. And this actually works much more stably. Why it doesn't work like this by default is a mystery to me.
Problem number two - there's a delay from pressing the button to the actual language switch, it's somewhat asynchronous, gets worse when the system is under load. In practice, this means you switch the layout, start typing, and get something like "xnо-то такое". Nonsense. That is, I press buttons in sequence, but they're processed by the system with different delays, causing buttons pressed later to trigger earlier. I'm living with this problem for now, fortunately it happens significantly less often.