I used this thread to pair my series 3 to my iPhone 11 iOS 14.4.2, after no success with an Apple support agent, 24 hours of unpairing, erasing data and trying different languages, I was able to download the update. I used Dansk as the language and Finland as the country and began installing the update, it did take about two hours to install and go through set up to actually use the watch. Make sure your watch is on the charger for the update. I also followed advice on this thread to not use my phone for anything else during the update. I’m so happy to be able to use my watch again as it was previously paired to my old iPhone that broke a few months ago.