CompareTag - NullReferenceException

Collider2D Obj = Physics2D.OverlapCircle(transform.position, 0.05F);

    if(Obj.CompareTag("SomeTag"))
    {
        isActive = true;
    }

NullReferenceException: Object reference not set to an instance of an object.

What am I doing wrong? How to fix it?

If Physics2D.OverlapCircle does not give you a collider, it’s because there are no colliders in the circle, as said in the doc HERE.

So you need to check the value first :

    Collider2D Obj =  Physics2D.OverlapCircle(transform.position, 0.05F);
 
    if(Obj && Obj.CompareTag("SomeTag"))
    {
        isActive = true;
    }