The integration between different Apple devices is unique, with the ability to interact and communicate very closely. It comes down to the details of being able to rely on each other for some security features.

This point can be seen, for example, in the integration between the iPhone and Apple Watch, where the latter is able to unlock the former. This unique ability is almost in doubt now, with problems unlocking the iPhone 13.

The ability to unlock the iPhone with the Apple Watch was introduced in April, and it has temporarily replaced Face ID.  Compulsory use of a mask came to destroy the ability to unlock a smartphone with the face only.
This handy new feature always works flawlessly, ensuring that iPhone users can do without all other forms of unlocking.  That record of perfection is now in doubt, with the arrival of the iPhone 13.
You are Reports are piling up It reveals that unlocking iPhone 13 with Apple Watch feature simply doesn't work.  When users try to activate this capability, a message appears indicating that this smartwatch cannot be connected.
The message in question is clear and states that it is not possible to communicate with the Apple Watch.  This scenario occurs in situations where the watch is already linked to the iPhone 13, and there is no logical reason why the connection should not occur.

From what was revealed, all attempts to find a solution to this failure were unsuccessful.  Even when you activate and deactivate some functions, re-pair devices or simply restart your Apple Watch, nothing seems to work.
This should be another case that Apple will be able to resolve with a simple update to the new iOS or WatchOS.  This fix should be rolling out soon, and may have already been included in iOS 15.1, which Apple is already publicly testing.