Can you Partition a Time Machine External HD to share with another Area

[Sarcany]

Microman wrote:
So a Big Sur computer, that has an external drive formatted as Extended, gets converted by Big Sur to APFS, and putting an important file or folder on the Time Machine drive might get eaten or written over by Time Machine?

The file won't get over-written.

But the backup daemon will not factor in that used-capacity from your other files when calculating the space available for a backup.

Eventually, this will cause it to throw a "disk full" error and stop backing up.

So, you prep the disk by erasing and partitioning it with two volumes. One for your Time Machine backup and one for your CCC clone. Don't use APFS "containers" if you see a message about that when you opt to partition in the Disk Utility in Big Sur. You want real "partitions" for this purpose.

And the partitions do not have to be of equal capacity. If your boot drive is 1TB, there's no particular reason why you need to allocate more than a TB to your clone. Meanwhile, Time Machine loves to gobble disk space, so it's a good idea to allocate more than the capacity of your boot drive to your Time Machine backup.