Categorize Individual Roblox Games Separately under Roblox as a platform
Seeing as though Roblox is starting to be a sort of platform for games as opposed to being just a game itself, I think it would make sense to categorize games that run under Roblox (such as Bad Business, Phantom Forces, etc.) separately from Roblox itself. This is purely for game-tracking purposes in game-tracking services that use IGDB as their database.

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OMGparticles commented
I feel like this is already supported through the 'game type' feature available under the General tab when editing a game. You can set the game type to 'Mod' and choose Roblox as the original game. It might be helpful though if they added something like 'User Generated Content', or 'Game within game' as an alternative to 'Mod' for games that act as game platforms, such as Roblox or Dreams.