Are you referring to paring the watch with the phone, or was it already done and just the syncing fails? In the second case, check out theSync / Connection Troubleshooting Guide.
Go to the phone Settings -> About Phone. Find Build number. On my phone (Pixel 6 Pro) I have to click Android version to see Build number. Click Build number at least seven times until you get the message that you are a developer.
After that you search for "Gabeldorsche" in the settings search function or go to Developer Options. On my phone it is located under System.
There is also link to an article explaining exactly what Gabeldorsche is, and how to enable it, in the previously mentionedSync / Connection Troubleshooting Guide.
Enabling the new "Gabeldorsche Bluetooth stack" option in the developer options of the phone fixed the BT connectivity problems too, on some phones at several users.
