What upgrades does this "Nightography" camera have over the S21 Ultra?

[DanielLoreti]

And is it something that can be added to the S21 line through software or is it hardware exclusive to S22?

 

[claykin]

The SD 8 CPU has a new image signal processor which Qualcomm claims offers 5x improvement in low light photography over the SD888 in the S21 series. So, I'm going to suggest no, the S21 likely won't ever be upgradable to the level of low light photography the S22 series can offer. Then again, I take 5x marketing blurbs with a grain of salt until I see real world results.