gadgetdad1 wrote:
Can I partition an external HDD to keep Monterey TimeMachine backups and newly installed Sequoia TimeMachine backups.
Are you running two different versions of macOS on this computer? If not, then why the separate backups?
I never recommend using multiple partitions for any drives. People usually discover much later that one or both partitions are too small.
With the APFS file system, you can instead create a new APFS volume which acts a lot like a partition, but doesn't require you to make any size restrictions for the APFS volumes (to use Quotas is tricky when it is for a TM backup volume). See this Apple article for details:
Add, delete, or erase APFS volumes in Disk Utility on Mac - Apple Support
Once I partition the new 14TB HDD, how do/can I move my Monterey Time Machine backups to the new partition?
No. You cannot modify any existing TM backup or you risk corrupting the TM backup. Leave the TM backup where it is if that backup is important to you.