Encrypted passcode

If FileVault storage encryption is enabled, then you are effectively an attacker here, and unfortunately for your efforts to breach and gain access to data you lack access authorization (the password), the authentication and the encryption is robust. There’s intentionally no back door.

If you had FileVault turned off, then most of the data is probably available. That data might be accessible using Target Disk Mode. That would usually work best with a cable from the old to the new, and with the HDD back in the old, and a more modern macOS install on the HDD or SSD in the new.

Transfer files between two Mac computers using target disk mode - Apple Support

Swapping the old HDD into a sled would be typical, as dozen year old HDDs are not known for their longevity. Or HDDs for their performance. I’d swap that HDD right back out of the new Mac, and replace it with an SSD.

And as a first step, I’d get a bit-level backup of the old HDD too, on the off choice the HDD is failing.

As for the password hint: Ones and zeros and megabits and kilobits and exabits, English and Western tack for horses, assorted screwdrivers, tools for drilling holes materials, and probably a few others.

The whole point of encrypting files is so that only people with the proper credentials can access them. If there were a way around it, it would be a way for people to steal data.

I don't believe there is a limitation on the number of times you can try passwords. Do you have someone who was in your life twelve years ago who might have some insight into your thought process from the time?

MrHoffman wrote:

As for the password hint: Ones and zeros and megabits and kilobits and exabits, English and Western tack for horses, assorted screwdrivers, tools for drilling holes materials, and probably a few others.

It brought something somewhat more uh, personal to my mind...

The hint is something you created. Knowing that, does it help you remember?