Except he did write something down:
(John 8:1-11)Now, I'll grant that it wasn't recorded, but we clearly see him writing here.
1 while Jesus went to the Mount of Olives. 2 Early in the morning he came again to the temple. All the people came to him and he sat down and began to teach them. 3 The scribes and the Pharisees brought a woman who had been caught in adultery; and making her stand before all of them, 4 they said to him, “Teacher, this woman was caught in the very act of committing adultery. 5 Now in the law Moses commanded us to stone such women. Now what do you say?” 6 They said this to test him, so that they might have some charge to bring against him. Jesus bent down and wrote with his finger on the ground. 7 When they kept on questioning him, he straightened up and said to them, “Let anyone among you who is without sin be the first to throw a stone at her.” 8 And once again he bent down and wrote on the ground.[a] 9 When they heard it, they went away, one by one, beginning with the elders; and Jesus was left alone with the woman standing before him. 10 Jesus straightened up and said to her, “Woman, where are they? Has no one condemned you?” 11 She said, “No one, sir.”[b] And Jesus said, “Neither do I condemn you. Go your way, and from now on do not sin again.”]]
And commanded Scriptures to be written:
Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea. (Revelation 1:11)
Moreover, as all Scripture is given by the inspiration of the Spirit of Christ, who says what the Lord wants Him to, then the Lord commanded all the NT to be written.
I have yet many things to say unto you, but ye cannot bear them now. Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. He shall glorify me: for he shall receive of mine, and shall shew it unto you. (John 16:12-14)
Thus RCs who employ the parroted polemic that argues Christ never commanded anything to be written down, nor did so Himself, thus the church cannot be based upon Scripture (though that is how its Truth claims were established upon), either rely upon the specious red letter hermeneutic even homosexuals employ, or they deny the nature of the Trinity.