FWIW, my own personal subjective experience and opinion.
While the same sensor model and size is used in the Mini3P,
M4P, and
Air 3, I have all three and to my eyes the imagery has steadily improved in color fidelity, noise reduction in shadows, better low light performance, and better detail in 48MP mode.
I can only speculate, but I assume the image processing pipeline has improved, the quad debayering in 48MP is better with more processing power, and other improvements downstream from the sensor.
Also – pure speculation – It's likely there have been some improvements to the sensor over several generations, and the
Air 3 could be using a more expensive version with better noise characteristics derived simply by binning, for example.