How these particular entity selected with contact field name works? From where these 4 relations are coming and can we make a new relation to add here ?
Tried various combinations but no inbound customer journey worked for me.

How these particular entity selected with contact field name works? From where these 4 relations are coming and can we make a new relation to add here ?
Tried various combinations but no inbound customer journey worked for me.
These relations are basically the lookup fields that you created contact entity. Create another relationship and that will appear in the list as well.