So I am having the exact same issue. I downloaded the Apple Support App on my iPhone and found a chat option.
I do not have a fix yet, but they did some basic troubleshooting which may work for some. One was to connect your phone to your computer over USB (I haven’t done that in years since I sync everything over wifi) and found the file on my phone. I tried to transfer it over to my computer, but it errored again. What this means is it is still trying to process the video into a timelapse video on my phone. It has not tried to sync the file to any cloud platform.
what this meant is it is now above the pay grade of the basic phone support people. They have now escalated it to their Creative Media area and gave me a business hours phone number.
not a fix, but positive steps in the right direction I guess?!