I have two macOS Mojave macs that back up to a drive. Now, when I’m trying to just grab “backups.backupdb” from one HDD to another,I have this error : copying is almost over and the size of the folder stars increasing,so it continues copying endlessly. I tried “Carbon Copy Cloner” and it refused to copy files even with all permissions in preferences : “Apple doesn’t not support third party utilities to copy TimeMachine Backups”
I wouldn’t bother copying. I realize you may have very compelling reasons to try, however.
While you are researching this, start a new backup on the new disk. Set aside the old one until you’re sure you no longer need those backups, then decide to archive it or erase it.
Lets say you have 100 files and time machine backs them up 24 times in a day (once an hour). Instead of a reasonable copy time, you have to wait 20x longer for this copy. If you check how many files you are backing up, the math goes against you being willing to wait quickly.
This backup system is designed to optimize time to restore and to dramatically conserve space on disk, not to be quick to copy a destination.
In summary, the leverage for this copy to work rapidly doesn’t exist so you pay a large time penalty due to how it’s engineered.