who vs whom

Please help. Thanks!

who, it said, had caused public disquiet.

This makes sense to me.

Grammarly suggests:

Whom should be used to refer to the object of a verb or preposition. When in doubt, try this simple trick: If you can replace the word with “he”’ or “’she,” use who.

If you can replace it with “him” or “her,” use whom.

Who should be used to refer to the subject of sentence.

Whom should be used to refer to the object of a verb or preposition.

Who would like to go on vacation?

Whom do you believe?