Crossfire function is AMD's patented technology. NVIDIA (NVIDIA) and Intel are not authorized by AMD (because they are competitors of AMD, it is impossible to obtain patent authorization), so the products of NVIDIA and Intel have no crossfire function (no hardware model).
Therefore, the situation of "centralized display, nuclear display and single display can exchange fire" you mentioned will only appear on AMD products, not on NVIDIA or Intel products.
AMD's current set display and nuclear display are both called APU, but this is just a different name, and the actual meaning is the same. AMD does not have all types of APUs that can interact with its own discrete graphics card.
Similarly, not all AMD discrete graphics cards can exchange fire, depending on the model.
Relatively speaking, the crossfire between discrete graphics cards is more significant, while the crossfire between APU (that is, centralized display) and discrete graphics cards is more gimmick than practical significance. Anyone who has used APU and discrete graphics card to exchange fire knows that the exchange of fire between them can hardly improve the performance of the game. It is not so much a practical effect as an advertising function.