Raise Dead even calls out not being able to revive undead, but Revivify does not. It's a creature turning into another creature either way.

What happens if you cast revivify on an undead?

If you cast revivify on a zombie, the creature returns as a zombie. The spell doesn't change creature type.

Can you revivify a zombie?

If you cast revivify on a zombie, the creature returns as a zombie. The spell doesn't change creature type.