What is the best way to back up a Time Machine drive

The easiest way to do what you want is to add another drive that Time Machine can use to backup your Mac.

Buy a second external drive and format it for Time Machine. TM can alternate the drives it backs up to.

You can also manually have TM backup to either drive anytime you wish.

Back up your Mac with Time Machine - Apple Support

Use Time Machine on your Mac to back up to multiple disks - Apple Support

I never backup a backup. If the original backup has any type of error or issue, I would only be duplicating that and might end up with two unusable backups.

One option would be to use Time Machine for one backup and use Carbon Copy Cloner to make the second backup (from the Mac, not from the Time Machine external drive).

Another option would be to make two Time Machine backups as described in Use Time Machine on your Mac to back up to multiple disks - Apple Support

See the following excerpt from that support article:

For extra security and convenience, you can back up to multiple disks. If you work in two locations, you may want to keep backup disks in both places.

Time Machine rotates the backup schedule among the disks. For each disk, Time Machine backs up everything that’s changed since the last time that disk was used. If you designated items that shouldn’t be backed up, the list of excluded items applies to all backup disks.

I do hourly Time Machine backups on one external HD that stays connected to my Mac.

Then I do weekly and monthly backups using CarbonCobyCloner on separate external SSDs.

The weekly clone backup says handy but off line and the monthly clone backup goes into the Fire Safe.

As mentioned CarbonCopyCloner can not make backups of your Time Machine backup.

den.thed wrote:

... and the monthly clone backup goes into the Fire Safe.

...

You may already be aware, but just in case, many fire safes are not rated to protect hard drives or SSDs in event of fire.

I once found a Silicon Valley company that I worked with had backups of both their business records as well as backups of software they developed that was a major component of a product they made stored in a safe that was not adequate.

Usual is multiple HDDs, with some of the HDDs kept offsite, and a scheduled HDD rotation.

If you have a firebreak or second building accessible on your local network, a NAS in the other area also works.

As stated get another drive. FYI CCC cannot backup the TM files.

Yea' you bet. The Fire Safe is in another building on our lot, so it is more for security than protection from fire.