Convert the keyboard key lookup to a map, mostly stylistic but I imagine it’s also easier to edit.
Not sure why there is a col and row class that manages cells if the layout is flat
Getters, setter, properties, functions and constructors are all mixed together, it's hard to read
A custom event manager is used, EventTarget is built into the browser not sure why it’s not used
Usage of `_` instead of `#` for private variables
It's not recommended to setup the elements in the constructor https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_custom_elements#implementing_a_custom_element
You can use `||=` for assigning to an undefined variable (if it's undefined)