Question How to detect when an object enters a socket?

For example,
when I put two blocks together, it would trigger an event or change the value of a boolean.

 

You can subscribe to the Select event on the XR Socket Interactor. This is triggered when a Grabbable locks on to a Socket. Whichever object is going to be reacting to this event will need to be dragged onto the event as shown here:



In this example, I am changing the material of the Grab Interactable at the moment that it locks onto the socket. Note: this would only work with a single grabbable and a single socket. A more robust system would be needed if you have multiple instances.