In Ephesians 6:21, whom does Paul send to tell the readers everything about him?

Answer: Tychicus

Paul sent Tychicus, 'the beloved brother and faithful servant in the Lord,' to tell them about Paul and to encourage their hearts.

“Tychicus, the beloved brother and faithful servant in the Lord, will tell you everything, so that you also may know about me and what I am doing. I have sent him to you for this very purpose, that you may know about us, and that he may encourage your hearts.”— Ephesians 6:21-22 (BSB)