https://www.vgmuseum.com/features/sgb/
probably this I'd wager
gameyob might already support automatically showing the game-specific borders, but the sgb had built-in borders for games that didnt have their own which gameyob wouldnt have. so you'd have to manually supply those
if
@Datbo or
@kazuya8 would like to elaborate on this... it shouldnt be difficult to convert the images on that page to a format that will work on gameyob. if you can't figure it out yourself then I can probably do it, but I need to know which borders you actually need