I'd even go so far to say that the only way something can be literally unreadable is if it is physically impossible to do so (e.g. unrecoverable data) or there

I'd even go so far to say that the only way something can be literally unreadable is if it is physically impossible to do so (e.g. unrecoverable data) or there is not yet any known way of determining the meaning of a given text (e.g. the Voynich manuscript). But of course that isn't what is meant when we say something is unreadable because humans don't deal in absolutes (though programmers sometimes do, which is why programmers are so fond of using overly noncommital language like "should" and "most likely").