Focus Sash is banned from every generation of 1v1, giving every mon basically a free turn as u live a free hit. However, it is still shown in builder under 'popular items'. New players who do not know this may use Focus Sash or other related items such as Charizardite X, which is banned in ORAS 1v1, in the teambuilding proccess, which can lead to confusion and a waste of effort and time for new players as when only after the team is built do they realise that the item is banned. An alternative to this suggestion is putting an ILLEGAL tag next to the item. Now that i think about it, there should also be an ILLEGAL tag next to Pokemon banned in a non-OU / UU etc format for the same issue. Maybe some moves in other formats will need the same treatment, tho that is rarer and does not apply to 1v1 to my knowledge.
tldr add illegal tag for banned stuff in teambuilder or move items to useless
tldr add illegal tag for banned stuff in teambuilder or move items to useless