Expansion Card Video Input?

Firstly, is it possible to take a video input from another computer through a FW HDMI Card? What about a USB-C card?

Secondly, how hard would it be/would it be possible to make an Expansion card that can do video input through HDMI / Display port?

Leme explain why I thought of this:

Because the FW12 has a 360 hinge, it can fold up into a tent to make a nice little portable monitor. I cary a FW12 and a FW16, and I was thinking if I am carrying two screens, it would be nice to be able to use both screens. Also, for people with Steam Decks / portable game consoles you could use a FW12 (or other FW) as a larger, separate screen for better ergonomics.

FYI, I have a FW12 I5 and a FW16 R7 7840 w/ R7700s, both running Linux Fedora KDE.