It’s been a while since I did Xbox memory mapping (One X) but IIRC there is approx 2GB of ram withheld by the system, and then an additional one or two can be recalled by the system for the purposes of running things like background downloads, party chat, video chat. That means that when your game goes to cert it’s checked to be performant under max OS load; so 6GB. This causes lots of issues (and is a pain as even MS’s analytics indicated this was a use case that appeared almost never. From what I have heard since, these TCRs/XRs/FTCs having changed much.