A field initializer cannot reference the nonstatic field, method, or property

Hi, I searched on the internet about this problem but the answers didn't help, so I'd like to ask you how to avoid this error. (I'm a beginner so please don't lynch me if it's a stupid question xD). I've created a class (Figure) which has a name, an int order and a transform and it has a constructor to give each figure its name and transform.

 public class Figure
 {
         public int order;
         public string name;
         public Transform tr;
         public Figure(string name_, Transform tr_)
         {
             this.name = name_; 
             this.tr = tr_;
         }
 }

I've declared 4 public transforms that I give to 4 figures, and then I created an array that I'll use later with those figures.

     public Transform SquareTR;
     public Transform TrapezoidTR;
     public Transform CircleTR;
     public Transform TriangleTR; 
 
     Figure SquareF = new Figure("Square", SquareTR);
     Figure TrapezoidF = new Figure("Trapezoid", TrapezoidTR);
     Figure CircleF = new Figure("Circle", CircleTR);
     Figure TriangleF = new Figure("Triangle", TriangleTR);
 
     Figure[] Figures = { SquareF, TrapezoidF, CircleF, TriangleF };
     rest of the code...

When I start the game, the error occurs: "A field initializer cannot reference the non static field, method, or property", for each transform and figure. I could fix this problem creating the figures in the Start() function, but I have to use them in the Update() function too. I could also make figures and transforms static, but I have to assign the transforms from the inspector (If I don't do that the NullReferenceException pops up). How can I fix this problem?