There is no way to set a digital input to Generic Input although there is code in dbus_digitalinputs.py for that type.
Apparently you can set this type from Node Red.
Is there a reason the GUI can't select that type?
This was mentioned previously:
https://community.victronenergy.com/questions/257500/venus-gx-digital-io-as-generic-input-in-node-red.html