How to know if gameobject is in a circle in my canvas?

Hi guys, I’m creating a 3d unity game where my player auto-aims the enemy inside a circle range in my HUD (in case multiple enemies are inside my target range, I’ll choose the cloosest one). So I need to know when an enemy (or a general gameobject) enters the (invisible) circle-range in the center of my camera. How can I do it?

Checkout OverlapCircle()