Is "Le Miserables" singular or plural?

Le miserable.........singular

Les miserables.......plural.

Neither. It's wrong. In French, le is the definite article, singular and les is the same, plural. Le Miserable is correct, for singular. Les Miserables is correct, for plural.

Both.....................

it is in error as written. It would either be Les Misérables (plural) or le (ou la) Misérable if singular. The problem is that misérable is actually an adjective, not a noun, so it actually means the miserable ones or miserable people, without actually saying one(s) or people (person). The unhappy, the miserables, the impoverished or the suffering, perhaps.

However, as with many adjectives, it can be used as a noun, but I believe that the gender of the singular would depend on the gender of the individual. Sort of like propriétaire (owner).

Neither, you have one of each. It is Les Miserables, which is plural.