After a couple emails with the company (they were super fast/responsive!) they sent me the pinouts.
Posting this here in case someone else searches this in the future:
There's also a capacitive touch output, which I assume is the remaining non-ground pin (3rd from the left), but I've not been able to find one of the Steam Deck caps for purchase anywhere (they have a lead coming out from the bottom which you need to solder).