There isn’t a blanket rule for all things, you have to go to each monster description. While I agree it wouldn’t work on a specter, it would affect a toxifier, for example.
Edit: and the paragraph after the on LokRobster quoted specifically denies it by college.
Quote:
Most magic is ineffective against specters,
but Communication and Empathy, Mind
Control, and Necromantic spells can affect
them.
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