Not what you're asking for, but another option is to use a DualShock 4 controller which also supports touchpad (which can be divided in left/right if you want). I've found a pretty decent amount of community support and often use the touchpad (or gyro) for mouse games, though it's not quite as comfortable as the Steam Deck .
(I'm sure Dualsense 5 works just as well but I can only speak to Dualshock 4, which you can find for the cost of a HDMI cable online).