It will be substantially better in low light situations, but less normal lighting situations.
If you take images late in the evening or at night then the pro Max will do alot better than the regular pro.
How much better we will see in the coming days, but the sensor stabilization with a larger sensor will have a huge impact.
But to buy such a big phone for such a special purpose alone is not understandable for me as the benefits outweighs the positives.
If you prefer Big! phones though, good for you, as you also get a better low light camera in that package.
*only the wide aka normal lens get stabilization+ bigger sensor, AFAIK.