Use bumper triggers on ROG phones.

[Vableme]

Let us use the triggers on ROG phones (1, 2, 3, and 5) on the camera app while in landscape mode to act like shutter button (take a picture).

[Aryan202]

By the way I remember reading on zentalk that someone mapped air trigger functions to camera (shutter etc) by adding stock camera app to game genie and accessing air triggers functionality via that
And Rog 5 already has that feature you're referring to by default