The S21 Ultra camera was a big improvement over the S20 ultra. It fixed a lot of the focusing issues. It is even an improvement over the note 20 ultra in terms of processing and colour production.Most if not all reviewers noted significant improvement. Again I have both in my house. Lol
Is the improvement like from 10 to 11? No. But 12PM is a refinement of everything that was wrong with 11 (which was a top notch phone in its own right). Bigger sensor and wider aperture allow from much better noise reduction without losing details especially when light gets low. That was my main complaint with 11…details are there with lots of noise. 12 PM fixed that. Portraits from the slightly longer lens are MUCH better. Don’t ask me why! It just is.
I would agree that low light photos are better on my 12 pro max than my 11 pro max. However I'm a smartphone enthusiast and see the benefits of minor year over year upgrades. The average user won't.