JSAUX HB1201S x Steamdeck - All work but HDMI

Not the first time I realize from other posts, but most solutions seem to be some magical plug-in order which I can't seem to replicate.

Just bought the JSAUX HB1201S, and plugged everything in. Mouse & Keyboard work, power seem to work, just nothing on the screen. Tried two different screens, 2 different HDMI cables. Tried restarting deck, dock, nothing.
The screen reacts when plugged in the dock (alternate between source mode, trying to find signal).

The steam deck never seems to detect any extra display in the display settings in desktop mode.

Any advice would be fantastic!