Pronouns are words used to avoid repetitions of a noun {see Subject Pronouns, A1 Level}.

Relative pronouns  are used to introduce relative clauses. They refer to place and time by  replacing the subject expressed in the main clause to avoid the  repetition of it in the relative clauses {see Relative Pronouns, A1 Level}.

https://open.books4languages.com/english-a2-grammar/chapter/relative-pronouns-of-place-and-time/