Which relative pronouns in clauses should act as components and which ones should not? Please indicate in which clauses you act or do not act as a component.

Pronouns, pronouns, just replace a word that has been mentioned before the sentence, so pronouns should be used as sentence components.

In clauses, only some leading words do not make any components and have no real meaning; Whether the leading words are meaningful or not, some can be omitted, while others cannot. There must be concrete examples to explain the details. Your question is too wide.

Relative pronouns can be used as subject, object (including prepositional object), predicative and appositive in clauses.