Does Jesus’ baptism in the Jordan “prove” that He was a sinner?
Just askin’
NO. Jesus said to permit it to be so to fulfill all righteousness. He was submitting to show what His followers should do.
Mat 3:14-15.
If someone says to follow Jesus or be like Jesus, He provided us His example. Had He not done this, you might think you don't have to. If you have confessed Jesus as Lord and have faith in Him, then unless you are on your death bed, you should attempt to get Baptized as your first act of obedience to God. Your faith is what saves you however, and not baptism. People that come to Jesus on their deathbed and other situations are still saved if they cry out to Him. If you've been saved for months, however and never get baptized, I have to wonder about your commitment to Him. We are commanded to be saved and then baptized.
Mat 28:19-20
Nope. Because we have the texts, and knowledge, that He did not sin. He is the only person documented beyond doubt to have not sinned.
14For the love of Christ controls us, having concluded this, that one died for all, therefore all died; 15and He died for all, so that they who live might no longer live for themselves, but for Him who died and rose again on their behalf.
16Therefore from now on we recognize no one according to the flesh; even though we have known Christ according to the flesh, yet now we know Him in this way no longer. 17Therefore if anyone is in Christ, he is a new creature; the old things passed away; behold, new things have come. 18Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, 19namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation.
20Therefore, we are ambassadors for Christ, as though God were making an appeal through us; we beg you on behalf of Christ, be reconciled to God.
21He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him. 2 Corintians 5:14-21 NASB
Scripture is crystal clear....only one person has ever been sinless....and that is Christ Jesus, the Son of the Living God.