adamf69,
Were you able to locate the option to turn on separation alerts for your AirPods Pro after ensuring your iPhone is updated to the latest iOS version? Also, a new update of iOS 16.1.1 was released today, so you may want to update again to be sure you're able to access that feature in Find My.
Did you follow the steps in the link posted previously to attempt to turn on separation alerts?
Turn on separation alerts on iPhone, iPad, or iPod touch
1. Open the Find My app, tap Devices, then tap the name of your AirPods.
2. Below Notifications, tap Notify When Left Behind.
3. Turn on Notify When Left Behind, then follow the onscreen directions.
4. To add a trusted location, choose a suggested location, or tap New Location, select a location on the map, then tap Done.
5. Tap Done.
You'll also want to be sure you have notifications turned on for the Find My app in Settings > Notifications > Find My in order to turn separation notifications on for your AirPods Pro.
Let us know what you find.
Cheers!