That's one thing that baffles me about MacOS. There is a lot of powerful stuff hidden behind keyboard shortcuts but there is almost no way to find them. It seems a colossal waste of energy to first implement them but then making it very hard to find them.
On iPadOS it's very similar. Sometimes I get two apps on the screen by accident but I have no idea how I did it and there is no way to find out how to do it if you don't do an online search. Good old drop down menus were actually good for something.
While it doesn’t solve the issue of not knowing a feature is there in the first place, if there’s something you’d like to do in an app, you can get a long way by hitting “Help” in the menu bar and typing it into the search field. If there are any matches for it you’ll immediately know you can do it, and it will open up the menu and show you exactly where it is (and the keyboard shortcut, if there is one).
This is the primary way I look for power-user or other non-obvious features in new Mac apps.
Menus are still superior to help search for feature discovery because they are an explicit navigable enumeration of the feature set surface; if help doesn't have the right synonyms, you'll be stuck, whereas menu item listing might hint at different ways to accomplish the same end goal.
FYI the search box in the help menu searches the rest of the menu bar. It's great for feature discovery if you think something might exist but don't know where it is.
My point is that menus work as a way of exposing functionality and making it discoverable through enumeration in a way that contextual UIs and fashionable techniques of the day don't.
This is in addition to access keys (also explained in the document above), underlined letters you can type to instantly navigate the menus and select even the items for which no shortcut is defined.
On iPadOS it's very similar. Sometimes I get two apps on the screen by accident but I have no idea how I did it and there is no way to find out how to do it if you don't do an online search. Good old drop down menus were actually good for something.