I have an iPhone 11 and an iPhone 13 mini with identical configuration and iOS 16.0.2 on both. On the 13 mini the system data grows to max, but on the 11 the system data stays at a stable level. The 13 mini is on 5G the 11 is on 4G. Fortunately, for me, a power off/on reset of the 13 mini brings back my system data to a reasonable value, but after a day or so the system data has reached max again. Since a lot of people have the same problem, I don't think that the problem is caused by 3rd party apps because we all have different apps on our phones. All tips about deleting the Safari cache and checking the memory use of different apps are almost meaningless. In the apps list usually the app size is less than 1 GB and the documents and data is less, unless you have stored a lot of media files. But these files are not a part of the grey colored part of the bar graph. The owner of the system data cannot be identified and probably it is the iOS itself that allocates memory without freeing it again. The system data is much bigger than almost any other app and/or data. At the moment, in my case, it seems that it may be dependent of which iPhone model you have and/or it may be 4G versus 5G dependent.