Circle.cs

public Circle(Vector3 center, Vector3 normal, int polyAmount, float radius)
    {
        this.normal = normal.normalized;
        this.center = center;

        var z = Vector3.forward;
        var dot = Vector3.Dot(z, normal);
        var y = z - dot * normal;
    
        if (dot == 1 || dot == -1)
        {
            y = Vector3.up;
        }

        this.vertices = new Vector3[polyAmount];

        var delta = 360 / polyAmount;

        for (int i = 0; i < polyAmount; i++)
        {
            this.vertices[i] = Quaternion.AngleAxis(-delta * i, normal) * y.normalized * radius + center;
        }
    }
}