iOS 18.1 added an implementation of the auto-reboot timer for locked devices we've been using in GrapheneOS since June 2021:
https://chaos.social/@jiska/113447894119816217
This was one of our early generation protections against forensic data extraction. We added a lot more protections this year.
iOS 18.1 was released on October 28, 2024. This has nothing to do with recent news coverage where cops are blaming imaginary features for devices not staying in After First Unlock state. Devices likely crashed due to one of many bugs which exist, including already patched ones.