What worked for me: Hard restarting my iPhone 11 Pro Max (Volume up button/Volume down button/press and hold Side Button until I see the Apple logo) Hard restarting my replacement Series 5 Watch (hold Digital Crown and Side Button until I see Apple logo) Turning on low power mode on my iPhone (I am not sure this matters, but another user in this forum wrote that it worked, so I thought, "why not?") Trying to pair again by holding iPhone in proximity of Watch and crossing my fingers. The new watchOS started to download to the Watch via my iPhone. Thanks!