A user on r/HomeKit has reported a new feature in iOS 18 for Smart Locks. The post shows an auto-lock option that allows to set smart locks to automatically lock after a specified time period, ranging from 30 seconds to 30 minutes.

The feature was works at least with an Aqara Smart Lock U200.

Post: https://www.reddit.com/r/HomeKit/s/8P13RVBs8f