Time Machine Disk won't mount on new MiniMac Pro 4. Correct disk password rejected.

I have a new MiniMac Pro 4, 2024. I have my old TimeMachine Disk (TMC) from my iMac 2017 (Intel) connected to the MiniMac.

However, I am unable to

1. Launch a Time Machine backup using the TMC Utility
2. Mount the TMC Disk using Disk Utility

In both cases, I am required to 'Enter a password to unlock the disk'.

That's a correct response, as I did encrypt the TMC drive when I first set it up.

However, the password I enter is rejected as incorrect. I am sure I have the correct password.

When I reconnect the TMC Drive to my old computer, the TMC Disk connects OK. I can initiate backups and review old backups. I'm not asked for a password.

I used Migration Assistant to set up the new MiniMac from the iMac 2017.

TMC Configuration

The file system on the TMC disk is APFS case-sensitive and encrypted.

On the iMac It's a USB 3.0 drive connected through a USB 3.0 Hub to the iMac USB 3.0 Bus.

On the MiniMac I've used an Apple USB-C to USB-3 adapter to connect to the same USB 3.0 Hub configuration.

I vaguely recall having this issue once before with my iMac 2017. I just kept trying the same password, and eventually, it connected as far as I recall.

Question

Is there a way to find the password in a keychain, as I'm sure I have the option checked: Remember this password in my keychain. But I don't see anything that appears to be the disk drive. What is it called?

Troubleshooting

1. I will attempt to connect the TMC Drive to another Mac, a Macbook Air 2019, to see if the same failure to connect occurs.
2. I will remove the USB 3.0 hub and connect the TMC drive directly to each of the three computers and observe behaviour.