Copying Mac Backup Drive - Time Machine Backup - Backups.backupdb - hangs at 5 seconds

I know what Apple recommends in their Support document you may have read, but I find Disk Utility's Restore function (Restore a disk using Disk Utility on Mac - Apple Support) easier, faster, and more reliable than copying Time Machine backup files and folders the way it describes. It will finish in a few hours, rather than a few days. That's how I move Time Machine backup history from a drive that has become too small for my needs to a larger one.

I don't know the reason Restore is objecting to the backup drive's format. Its format and partition map should be the same as what you described for the new one. That's nothing new; TM has always required it. If it was not the correct format, Time Machine should never have been able to use it to begin with, and as you know you can't change its format without erasing it.

I don't have an explanation for that apparent conflict. The best I have to offer is to begin a new set of backups using the new drive. Set the old one aside until you are reasonably assured you will no longer need its backup history, then erase it and add it to TM's rotation.

Edit: you don't really need to erase the old one. It's just my opinion that if you have not needed to restore an item backed up ages ago, it's unlikely you will ever need it. The overwhelming number of backed up files (which can number in the millions) is the reason copying Backups.backupdb using the Finder takes so long. Unacceptably long... but again that's just my opinion.