Time Machine drive setup question

What does Time Machine do to set up disk drives?

I just initialized a (previously used) hard disc (not SSD) and created an HFS+ filesystem on it. Time Machine recognized the new drive popping into existence, and offered to set it up as a time machine backup destination. I agreed, and was brought to a brief configuration page. I turned *off* disk encryption, and clicked to set up the disk.

It then brought up a progress bar, 'Preparing "HHH5"' (HHH5 is the name of my volume.) It flashed the progress bar back and forth across the bar extent a few times. Now the progress bar is stuck at roughly 45% of the way across.

I did the same thing earlier and left it sit for about an hour and the bar did not move any further.

Is it possible that it is running an Erase cycle on the drive? The drive is 12 terabytes so erase would take rather long, if that is what it is doing.

If it were for some reason writing complete HFS+ data structures across the drive, I would have expected the progress bar to move over the course of an hour.

MacOS 15.7.2 (Sequoia) -- so 12 terabytes should certainly be supported.

Note that this is *not* the "Preparing backup" step. You do not get to "Preparing backup" until after the drive is initialized. For example at this stage, there is no Time Machine Options button.