Indeed not possible with the i4. On top of that I think you also need another type of wallbox.As far as I know, the EV6 and Ioniq 5 are the first cars to offer V2L and V2V function.
But the point is not to use them as a "home battery". You can just plug another device, or another EV, into the type 2 socket of the car with an adapter.
V2H (Vehicle to Home) is what you are looking for, and I don't think that any compatible car has been released yet in Europe.
Regarding the i4, it's not available and probably will never be (I guess that there are some hardware specifications to meet)