An interesting question @Jensonator
If you have Bixby Voice on your phone and have activated the Hi Bixby wake function you could try.
I know of no other setting within the phone to reject calls apart from swiping to reject , running your hand over the screen or turning it over.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "