Navigable by keyboard
by default? In Windows you hold down Alt and letters start being underlined so you can use the menus. On a Mac, assuming I haven't turned on any a11y features, how do I open and peruse the menus or, just as importantly in the modern era, navigate the random buttons every app has strewn around the top part of windows where the title bar used to be? e.g. in Messages there's a "New chat" button, a "Video Camera" button, and an "(i)" button in that top bar. Some might have direct keyboard shortcuts a user could have memorized like ⌘-N for New, but that's not what I'm asking. I'm asking how you navigate the UI widgets themselves.
Also, dialogs? Open TextEdit. Hit ⌘-O for Open. Hit Tab. For me, default settings, that focuses the Search field. It doesn't visibly move the focus to any other control. After screwing with it for a while, it seems like if you hit Tab two times, nothing appears focused, but then if you use Up/Down arrows at that point, they are now able to select items on the sidebar, then another Tab moves focus to the main file browser, and from there the Search again, and now focus cycles between those three. But there's still no way to access any of the widgets up top. So, it's half-assed and undiscoverable.