Honestly, the closest thing to "a 3DS game engine that isn't Unity" I can think of is SmileBoom's "PetitComputer ver. 3" (known as "SmileBASIC" in the US).
Would that be a good one?
@BigOnYa, when your wife kicks you out BOVONO Prefabricated Tiny Home, Mobile Prefab House with Lockable Door and Window, Outdoor Storage Shed with Restroom & Cabinet, Perfect for Hotel, Kiosk, Booth(19 x 20FT) https://a.co/d/ab1dd5t
@K3Nv2:
@BigOnYa, when your wife kicks you out BOVONO Prefabricated Tiny Home, Mobile Prefab House with...