With TM, it being read only may be part of the issue. It is also a special APFS volume type just for TM backups. I think that would be enough to stop copy access at of a complete volume level or even complete snapshot. But you could copy folders from a specific snapshot and maintain permissions etc. using a tool like Chronosync.
CCC can backup of the latest snapshot of a CCC backup volume. That produces a copy of the snapshot. Not the same as copying the whole volume, but maybe all that you need.
I am not aware of any tool which can copy a volume complete with snapshots. There are, out of my comfort zone, tools for copying a whole partition - which in this case would be an APFS container with one or more volumes.
