Are you still having issue?- I have a iPhone 16 pro that reboots on its own. Like you said I did not seem to notice it do this on IOS 18.0.1, I first noticed it on IOS 18.1 , however naturally as I am sure you probs know IOS 18.1 was supposed to fix this issue and I think it only fixed the issue for certain devices clearly, and clearly not all of the iPhone 16s like it said it would. I erased all content and settings on my iPhone set the device up as new and a couple of days later the issue persisted again, and then IOS 18.1.1 came out and a couple of hours after the install I have still been experiencing the issue, my device passes diagnostics every time indicating no hardware failure though.