The Unaffiliated selection in Seat Affiliations is system defined and is set to not show as in most cases no one wants to see anything in that spot.
However you can create a similar affiliation in settings under Home -> Settings -> Seat Affiliations. For example we can create a label Not Affiliated on your OBG.
Then edit the seat and change the affiliation to the new label.
The seat name now is listed with the custom label.