Backlog refinement is not mandatory as per Scrum and is considered a complementary practice. This is my understanding, however, I found myself in a position having to defend this and the counter argument that the other person made was that, since Backlog Refinement is mentioned in the Scrum Guide, then it is a part of Scrum.
If the intention is to help someone learn the correct thing, then how would you convince them that Backlog refinement is a complementary practice, when they quote the Scrum Guide against you?