Try being more familiar with the Bible John 6:15 occurs after Matthew 12. In Matthew Jesus walking on the water is in chapter 14 and that is after Jesus is accused in Matthew 12 of doing His miracles by the power of demons.
Chapter 12 in Matthew is the turning point of Jesus and His ministry.
Jesus' ministry looks no different after Mt 12 than it does before.
After Mt 12, we find large crowds gathered around him (Mt 13:1) whom he taught in parables
(Mt 13:3), teaching at the synagogue in his hometown (Mt 13:54), feeding 5,000 (Mt 14:19), teaching the Pharisees and teachers of the law (Mt 15:1), healing many (Mt 15:30) feeding 4,000
(Mt 15:35), teaching the Pharisees and Sadducees (Mt 16:1), healing boy with demon (Mt 17:15), large crowds and healing (Mt 19:2), large crowd and healing (Mt 20:29, 34), and then to Jerusalem for his sacrifice.
And you did not address Jesus not offering Israel a Messianic kingdom and rule!
Jesus rejected their offer of Messianic rule (Jn 6:15, 18:36 ) when they were going to take him by force and make him king.
Jesus said that his kingdom was
not an earthly kingdom, that it was from another place (Jn 18:36), that it was spiritual, an
invisible kingdom (Lk 17:20),
within (Lk 17:21) the hearts of those where he reigns and rules.