Your post is very light on details. Did they just place a new password on the device itself? If so, you can still use the laptop if you reinstall MacOS. It is only is rendered a brick if the attacker signed into their own iCloud account and enabled Find My, OR the attacker enabled Find My & enabled the recovery key feature on the existing Apple ID (meaning Apple can't let you log into the account without the key).

This was on OS X with one of the older touchbar Macbook Pro models, but there's some kind of password protection which can prompt you for a password before the usual visuals of the OS booting up.

Pretty sure this is FileVault full disk encryption.

And so you can still use the computer just not keep your data.

No, it's also possible to set a firmware password, which pops up if you try to boot from any disk other than the startup disk. If you also can't log into any user accounts on the startup disk, there's no way in!

Apple is right here though.

Those cards are easily forged and there is nothing you can realistically do to prove the laptop is yours without also allowing thieves/criminals to prove it's theirs. And so they have to err on the side of caution.

The onus lies on you to keep backups.

You can't backup a laptop, only your data. The laptop costs a lot. What Apple was "protecting" is the hardware value of the laptop, not any data.

Also, Apple eventually unlocked the laptop.

But you can always boot into Recovery mode and wipe the disk.

In this case you are wanting to keep the data as well.

There was no interest to keep the data, only the hardware, which Apple initially refused to unlock. I wanted my parents to be able to do this via Apple support, and not by themselves.

My experience has been different - Apple support asked me to email them the invoice copy of purchase to verify ownership of an Apple device.