Sorry to hear that, I don't have the pleasure to know what happens to those originally unaffected but seems like everyone is now on the purple boat. TBF, I am having a 1/8 chance of having a pure black picture if the camera decides to do so with a lower ISO. But the darker the scene, the likelier it will resort to high ISO and that is confirmed to be purple.My unit never have had this issue in iOS 18.1.1 and all versions below: in all the full dark shots @ 30 sec exposure the ISO was around 10k - 12k.
Once I have updated to 18.2 and above, the ISO for the same test shots went down to 6400 and also blue / red smudges started appearing.
With a moderately super dark scene (No idea how to quantify), such as under a few blankets or in a drawer that leaks light etc, I have from time to time drawn a pure black picture.
As usual in real life you will hardly have a pure black scene anyway and I feel that it should be the case of the very dark and maybe there are cases where you will have good luck with ISO2500, 1500, etc that begets you a better chance of no purple.
Anyway its a shoddy job, I have gotten over my grief with Apple, I am really tempted to trade in for a 17 Pro and testing every unit while at the store and just ripping through unit after unit to get a pure black one or if not I will just return everything to the store without a purchase! That will be my revenge.