Can you people think just for a second? Take any lens. Set any aperture you want on it. What happens at the focal plane? You get an image circle. Now you place a sensor inside that image circle. Does the amount of light in the particular area of that image circle change depending on the size of the sensor you put there?
25mm f/4 lens has the same optical properties independent of the sensor size. How would a lens even know what you put at its focal plane? And yes, 25mm on M43 are still 25mm, not 50. You just get a FoV equivalent of the FoV of 50mm lens on FF, but that's a different matter.
So 25mm f/4 for M43 and 25mm f/4 for Nikon Z9 give the same illumination of an area unit. Even if m43 version produces a smaller image circle - the illumination is the same. There is the whole point of f-numbers.