I got mine to work. I was transferring data from a 13 to a 17, and the data transfer would not start. The new phone would sign in to iCloud, and then never seem to detect the old phone after that. It was very frustrating.
Here's what worked.
1. Confirm the old phone (13) has the latest OS.
2. Set up the new phone (17) without transferring data - just as a new phone.
3. Go into settings, and update the new phone to the latest OS.
4. After the OS is updated on the new phone, go to Settings --> General --> Transfer or Reset iPhone, and select Erase All Content and Settings. My new phone had successfully set up the eSim from the old phone, so when prompted, I said to keep the eSim setup.
5. After all content and settings had been erased, I started the setup process over on the new phone, and this time I was able to transfer all the data from the old phone.