The yellow areas in the pic below are my guess as to what seem to be the standing room and party deck areas.
There was this report from a couple years ago alluding to buying tickets for these spaces:
What's also interesting about the report from Jason Wolf, in regards to the potential new stadium in Orchard Park, is the fact the new stadium could have room for 5,000 more people with a standing-room-only party deck.
If you're unfamiliar with a party deck, the most famous usage of them have been at AT&T Stadium, where the Dallas Cowboys play.
They're situated in the end zones and are first-come, first-serve for the front of the party deck, with pretty amazing vantage points.
Would you buy a ticket for a party deck at a Bills game, even if they're standing-room-only?
https://wyrk.com/buffalo-bills-party-deck/
Since Legends is running the show, I’m linking the SRO page from ATT stadium:
https://www.dallascowboys.com/tickets/standing-room-only-tickets-faq
This Reddit thread is insightful and humorous at the same time: