How to help newly adopted BSH feel less scared

We adopted a 4 year old boy. We got him home 3 days ago and he has been hiding under our bed. He has been ueating and pooping and doing zoomies when left alone.

We sit in the room and mind our own business to help him get used to us. Is there anything else we can do to help him adjust?

We are seeing him less terrified as each day goes by and he peeks from under the bed and observes us.