The photo of the entrance hall will be placed automatically in the additional photos that appear last in the Photo Tour since "hallway" isn't a room that is included in the selection of rooms that Airbnb provide and as @Andrea6232 says, no "à la carte" room creation possible I'm afraid😉
Sometimes these entrance halls serve as a lobby or a shared space for more than one guest, so there should be an option to include such a space. It’s not just “additional photos”—sometimes it’s more critical to know about, as it can be an integral part of the listing.
Please submit this as a suggestion to Airbnb. I’m sure others have done so and will continue to do so as well.