Didn't we used to be able to type "entity:node/####" in a typeahead field?
Ooooooooookay.

The entity:node/[node_id_number] only works in a Drupal link field. It does NOT work in a Drupal entity reference field. 

Although both of those fields feature the typeahead function and link to other nodes, you cannot use  entity:node/[node_id_number] to fill in an entity reference typeahead field.

Thanks @Clive for making me clarify my field types and start down the path to seeing my wrong assumption.