Jesus gives his disciples authority to forgive sins in John 20:23. If delegated forgiveness is possible for the apostles, isn’t it possible for Jesus without his being God?

A good point, and the reply is that John 20:23 gives the apostles authority to declare forgiveness in Jesus’s name, as his agents, whereas in Mark 2 Jesus claims the authority on earth as the Son of Man in his own name and proves it by a miracle. The scribes’ objection is precisely that he is not invoking anyone else. Matthew’s version, where the crowd glorifies God for giving such authority to men, is the best text for the agency reading, and the Trinity case addresses it directly.