- Tab to move across fields.
- Left-to-right, top-to-bottom focus.
- Space to toggle togglable stuff.
- Alt-Down Arrow to deploy drop-down stuff.
- Arrows to move around.
- Enter/Esc to accept/discard a modal.
Or maybe I misunderstand the things you call "mouse things".
Keyboard design is much more, its also about how and where to place items, how things should move... it's a whole world. In the mouse world we have "discovered" those things and now we "just copy" other designs that we know work fine.
If this grid a central component of the application and navigation inside it is very common, I would argue that there should be a way to quickly move around the cells. The "how" is up to the specific application and the paradigms it promotes. For example, line navigation in vim is possible with "<N>G", but such a shortcut would seem absurd in another application.
- Spreadsheet-like stuff: arrows, PgDn, PgUp, Home, End, … move inside of it.
I don't know about 'first' because I don't see a reason to privilege keyboard workflows over mouse workflows given how ubiquitous the latter is but Windows has had, for literally decades a 35 page Keyboard UI spec. They've put a fair amount of effort in applications being navigable in a consistent way.
https://learn.microsoft.com/en-us/previous-versions/windows/...
https://www.w3.org/WAI/ARIA/apg/practices/keyboard-interface...
I mean something like this (my wip keyboard-first file manager): https://ibb.co/G3WBW5C1
The hard part is, there seems to exist no UI & UX design language I can follow to create a nice keyboard-first app, so I have to think through everything (which is fun but tiring).
Your resource mostly describes how to make keyboard-based workflows accessible. But just because the full functionality of an app is keyboard accessible, doesn't mean that it works as well as the pointer-based approach - especially if you have an app with multiple menus, sidebars, headers, footers etc. Maybe you could tab through everything, but a pointer will be faster. This is where a "keyboard-first UX concept" is missing (from GP).
I think an interesting idea to solve this would be a "focus navigation mode". Enter this mode with 1 shortcut and then navigate between items with a few keys; like a combination of mnemonics and screen reader navigation e.g. jump between headers with "h" etc.