Unable to complete data transfer IPhone 6s to IPhone 12

I’ve attempted more than x5 unsuccessful times and many hours to use the quick start data transfer method.

Details:

Current iPhone: IPhone 6s running 14 iOS 64G

New iPhone: iPhone 12 128G- I assume would be running higher then 14iOS

I transferred my SIM card over to my new phone prior to starting the transfer and both phones were next to each other and charging throughout.

I have never used iCloud and am not keen to as its not a complete data transfer.

I also attempted a full backup of my old iPhone to iTunes with nil success (error message came up during the backup)

Both phones have been connected to wi-fi throughout.

The quick start method works initially however gets stuck on “Setting up your Apple ID” for approx 35-40mins, after this time I am taken through the usual terms and conditions, Siri set-up,

locations, app sharing information prompts until then suddenly receiving “unable to complete data transfer” and forcing me to reset the entire iPhone 12.

Frustrating! And no one will help me through this process in store at Apple due to COVID restrictions and I am continually directed back to online Apple support. Any suggestions would be appreciated. I just want to be able to use my new phone.