Installing Mac OS High Sierra

Hi there Parallels Forums
I've recently upgraded my Mac now running Big Sur, but my legacy accounting software won't run. I've installed Parallels for Mac Desktop 16 as a trial to see if I can get it working here. I've run the OS install from a bootable drive and chosen to restore from Time Machine backup, but it says "you can't restore this backup because it was created by a different model of Mac". Any ideas? Thank you...