If you've had your iPhone set up to unlock with your Apple Watch and recently upgraded to an iPhone 13, a software bug may have prevented you from continuing to use this. Thankfully, a fix is here and once you install it, you shouldn't have to resort to Face ID (or worse, typing in your passcode) anymore. The latest iOS 15 update (iOS 15.0.1) is here and according to the changelog, it brings bug fixes "including an issue where some users could not unlock iPhone 13 models with Apple Watch."
Apple added the unlock with Watch feature in watchOS 7.4 earlier this year to make it easier to get into your iPhone while you're out and masked up. This feature later got broken with a subsequent iOS and update and required another over-the-air package to fix. Apple recently acknowledged that this was also not working on some iPhone 13 models, and said it would roll out a solution soon. The iPhone 13 only started being available on September 24th, so this issue was at least caught early. Though it's nice that the update is here days later, it's interesting to see the trouble the company has had with this feature in the last few months.