You need a high-speed 15 second GIF/mp4 screencast with keypresses visible (maybe use a trial of Camtasia) if you think all the hotkeys should be used a lot. At least a screenshot or two of a "document" in progress! (Screenshots here apparently: https://twitter.com/Zeminary/status/1432195697449766921, though it would be cool to show a complex document.)

Also, set the title attribute on your navbar item divs and modal editor toolbar buttons, otherwise there is no idea what each does. Clicking the '?' for help is useful, but I still don't have any idea what menu icons do even after looking at the source for some of the function names. I don't even see the Unicode characters for the file & modal editor, they are just the U+25A1, white square (representing a missing ideograph). I doubt many first-time visitors / potential users will even click to view the modal editor, it seems great.

I think I get the idea of each square being a cell, not showing empty cells like Excel does for a blank page. Then you fill in each cell in the grid and add/remove rows/columns as desired. So it could wind up looking like a Trello board if you wanted to use it that way.