backup capacitive touch button with momentary switch
pin 12 &quot;OPDO&quot; is an open-drain output, wire the mechanical button in paralell with pin12 and ground and configure your auduino input with the pull-up enabled.
In the BA6 package it doesn't have the &quot;OPDO&quot; terminal, you could connect the switch  (and a pull up or down)  to the AHLB input. that should result in the switch causing the output to switch states when activated.
Another option would be to use a dual-throw switch between the touch output and the device input allowing the switch to override the touch output. or a switch and a gate could be used for much the same effect.