The definition of functional in the context of the discussion is that in works in the way the manufacture explicitly designed it work, in a standard industry practice fashion, not as an unforeseen bug or malfunction.

Not some abstract notion.

So not enumerating as a drive, and not allowing you to read even valid blocks is ‘working’?

Yes, same as a facility self-destructing, if it was programmed to do so, is working as per its spec.

And what spec requires that? I have yet to see one.

The manufacturers'.

Cite? I have yet to see that actually documented anywhere, and you keep avoiding actually referring to one either.