I figured out very early on Windows (this was the days of 3.x) that the Alt key could activate the menu and then let you browse the items with the cursor keys, and the underlined letters (which idiotically have been hidden by default more recently) work in combination with Alt to activate UI elements. I couldn't figure out how to do the equivalent in Mac OS. You had to inspect each menu first with the mouse (and hold down the mouse button while doing so), and hope that there was a keyboard shortcut assigned to the items you needed. It's possible to use Windows almost entirely without a mouse, although I've only had to do that to install mouse drivers or reload a glitched one. The same can't be said for Mac OS.

Some of the Finder keyboard shortcuts seem very counterintuitive; for example, the arrow keys move the selected item (same as in Windows), but although opening the selected item(s) is a very common task and one would expect that to be mapped to a very common key like Space or Enter like all the other file managers I've used, I believe one of those initiates a rename (a relatively uncommon operation) and the other does nothing, and the actual shortcut to open the selected item is Command+DownArrow or Command+O. I guess they make sense in their own way, but apparently I'm not the only one who finds this very unusual and confusing:

https://apple.stackexchange.com/questions/6727/why-does-the-...

https://superuser.com/questions/59007/enter-to-open-a-file-i...

https://superuser.com/questions/176450/open-file-shortcut-fo...

https://superuser.com/questions/134892/how-to-open-folder-wi...

https://superuser.com/questions/119871/how-do-you-open-a-fol...