The assertReadConcernSupported method is only used by the AutoGetCollectionForRead* family of AutoGetters. As a result, normal AutoGetCollection calls are exempted from that check.

For SERVER-77507 we integrated the assertion check into collection acquisitions and had to exempt writes from performing that check. Ideally, we would want to expand that assertion to everyone but doing so leads to this code causing issues. The transaction is writing to the config.transactions collection with the original read concern settings, leading to this assertion being hit.