i currently use a Asus ZenBook DUO -
the main screen is a 4k oled (very nice if dark surrounding - not usable at sunlight)
and in the bottom half it has a 4k-wide and 1/2 height LCD -
and the keyboard is in the bottom half.
i like this layout and the second screen very much!
Somewhere on the forum, there are posts of a screen made to go next to the touchpad. It was awhile ago, but I think it was an e-ink screen, connected to one of the input module’s spots, so using USB 2.0. That was the most advanced screen I recall seeing. Which is pretty far off from what it sounds like you’d want.
so seems that is a bigger project i have to start myself
my current prefered way would be to have a full screen in both laptops sides - and an external keyboard.
that makes it much easier for a good ergonomical setup..
and i think that this option maybe is even easier than the special bottom layout.
as now i would need to exchange the complete bottom input-part..
i hope in the late summer i find some time to start digging in the documentation and options to do this..