Grab an object only while pressing and holding a controller button in VRTK v4

To get rid of the grabbed object after the controller button is released:

Step 1. Find the button action

1. Find the desired button action in “Scene/VRTK Setup/InputMappings/UnityXR.OpenVR.LeftController”
2. Add a item for the “Deactivated” event
3. Drag “LeftInteractor” from Hierarchy to Inspector to fill in “None (Object)”
4. Choose “InteractorFacade/Ungrab ()” on the right

Step 2–4. Add an event handler

Thereafter you may repeat 1–4 for the right controller to achieve the same effect.