As a system macOS definitely has some holes in keyboard navigation, as well as a couple corners which are KB-navigable but the way to focus them is not immediately obvious.
On the app level, keyboard navigability depends on the developer. If they take the time to dot their I's and cross their T's it's between decent and great, but if they don't care it'll be bad.
"Some holes"? That's an understatement.
There's no option to bring up a context menu with the keyboard. And there are no keyboard accelerators _AT_ _ALL_. Windows will underline the shortcut characters when you hold "alt".
MacOS has intentional holes in keyboard support. You have to go into settings and turn on a config for keyboard navigation to reach all elements. Apple intends for most users to navigate with a mouse.
It’s in the accessibility settings.
https://support.apple.com/en-za/guide/mac-help/mchlc06d1059/...