The same answer will be given as to your 8K video recording post. The iPhone 16 Pro/Pro Max shoot in 4K video only [up to 120fps].
That is the highest hardware specifications Apple has determined. There is no app or ability to shoot in higher resolutions.
if you need higher resolutions, our suggestions is to
A. Wait until Apple has announced an iPhone that can shoot in 8K [Apple is not a camera company. When Apple does offer 8K, there will be no in between. Its either 720p, 1080p, 4K and 8K. There will never be an app or ability that can provide 6K].
B. Purchase an Android phone that officially shoots in 8K 30fps resolution
C. Purchase a DSLR camera