I can confirm that despite multiple efforts spanning over 48hr, the only way I got the update completed on my new Series 5 Stainless was to setup using a wiped iPhone 7 with iOS 13, and then unpairing and pairing with your chosen iOS 14 device. No help from online support who prompted to have it sent for “repair”. This is by far the most reliable method for kickstarting the update on your chosen device. Ensure you’ve also factory wiped your Apple Watch too (if it’s new from box and hasn’t been set-up before).