Using Intego personal backup to same disk as time machine

I'd like to use Intego Personal Backup to make weekly mirrors of my MacBook Pro running OS 11.6, and to do it to the same USB3 drive connected to my Mac. It's large enough, but my time machine backups are encrypted. When I set up Intego Personal Backup to copy a mirror onto the USB3 disk, it tells me it cannot reach that disk. Meanwhile, my Mac continued to back up to the same disk using Time Machine.

I also notice that I can't see the whole USB3 disk in Finder. It only shows the individual backups for Time Machine.

A couple of things occur to me as possible problems.

1. Do you think I need to partition the USB3 Disk so the time machine backups are separated from the Intego backups?
2. Could the problem be that the USB3 disk is encrypted since I asked Time Machine to create encrypted backups?

Thanks,