Can't restore from hard drive backup, but doesn't give error - just gets stuck half way through (NOT iCloud)

Hi all and thanks for reading!

I am using the latest iTunes on Windows 10 Pro with an iPhone 11 Pro Max running the latest iOS.

I backed up to iTunes using "This Computer" (and "Encrypt local backup" was enabled). It was successful, and the stored backup is around 186gb (it seems to be intact, with the usual files - Info.plist, Manifest.db, Manifest.plist, Status.plist).

I then did a full "erase" on my phone, and then am trying to manually restore the phone. I click "Restore Backup" in iTunes and choose the latest backup. It asks me for the password and I type it in. Then it pops up a window that says "Restoring iPhone from backup..." and then after about 45 minutes the progress seems to get stuck. I have just left it go several times - once for 12 hours! And nothing. It doesn't move.

I have plenty of hard drive space left. (600Gb) I'm not sure what else could be happening.

I have run the "iPhone Backup Viewer" software on the backup files, and I was able to read them all fine and extract contacts, notes, photos, etc etc. But that program can't actually restore my phone, unfortunately. I wish there was an option to "Create new backup that isn't screwed up". :-)

If anyone has any ideas, I'd love to hear them!

thanks

Toby