What crown does 1 Peter 5 say faithful elders will receive when the Chief Shepherd appears?

Answer: The crown of glory

Elders who shepherd God's flock willingly will receive the crown of glory that will never fade away.

“As a fellow elder, a witness of Christ’s sufferings, and a partaker of the glory to be revealed, I appeal to the elders among you:”— 1 Peter 5:1 (BSB)