> The problem is that's not going to be an easy thing to remember. It's not an obvious hotkey and nor is it even memorable that the hotkey even exists. There's no UI hints that it does.
While I think Apple's UIs do have annoyingly hidden functionality, this particular one is something you can learn by using Finder -- it's the keyboard shortcut for "Go to Folder…" in the "Go" menu. A lot of the "View" and "Go" keyboard shortcuts there work in file picker boxes, but it's true you're not going to be able to do actual file management there.
A lot of "hidden" keyboard shortcuts in macOS really aren't hidden, though; they're either right there in the menus or in the Help menu. If you're in Finder, the first item in that menu is "macOS Help," which opens a user guide…and that User Guide talks about a lot of things. And, it also links to the fairly extensive "Mac keyboard shortcuts" support article. This may be the technical writer in me, but I kinda wish people would read manuals a little more than they do. :)
While I think Apple's UIs do have annoyingly hidden functionality, this particular one is something you can learn by using Finder -- it's the keyboard shortcut for "Go to Folder…" in the "Go" menu. A lot of the "View" and "Go" keyboard shortcuts there work in file picker boxes, but it's true you're not going to be able to do actual file management there.
A lot of "hidden" keyboard shortcuts in macOS really aren't hidden, though; they're either right there in the menus or in the Help menu. If you're in Finder, the first item in that menu is "macOS Help," which opens a user guide…and that User Guide talks about a lot of things. And, it also links to the fairly extensive "Mac keyboard shortcuts" support article. This may be the technical writer in me, but I kinda wish people would read manuals a little more than they do. :)
https://support.apple.com/en-us/HT201236