Unfortunately, until version 9.1, which had permissions on telephone functions, I could only reject the call. Due to the new security policies imposed by Play Store, these functions were eliminated.
I have tried to give some call alert function by capturing them from the notification bar, but depending on how the notification is created, it may or may not work correctly. According to the application that handles the phone, I have had good results with:
Also, if the call action is in the call notification, the audio will never be transmitted to the smartwatch.
Usually devices that are prepared for this will not need any extra application, check this thread that may help you in your problem: