I had this same issue today when I brought my new iPhone 8 back home. I traded in my 6s, so they did a factory re-set before I left the store and I kept my old phone there with them.
I backed up my iPhone 6s this morning, so I had the backup on my computer already. After installing the new iTunes and plugging in my new phone, I got the error listed above about the backup "being corrupt or not compatible with the new iPhone". Here are the steps that solved it for me:
On new iPhone:
-went through the setup manually on the iPhone as if i was setting it up for the first time.
-on the new home screen, I went to <<settings<<<general<<<<software update
-I updated and installed the new software on the iPhone itself.
After Installing New Software on New Iphone
-open Itunes (make sure to have the latest version)
-plug in new iPhone
-there will be an iPhone icon in the upper left (under the play/pause section)
-click on the icon to bring you to the next screen
-On the next screen under the "Summary" tab, you will see the "Backups" section
-in Backups under "Manually Backup and Restore" select "Restore Backup". This will prompt you to choose the backup you most recently did. I backed my phone up to my computer, not iCloud. But you will see the option of where you saved it last.
-Your phone will then automatically go into the restoration process.
Hope this helps!