I am totally lost about what you want to do exactly...
void[] makes no sense, since void is the absence of type, used only in function declaration to mark them as not returning a value.
And you probably want to declare this array at the global level, because where it is currently, it is used before being declared (even in JS it is mandatory!). Same for your count variable, reset on each call of the keyPressed() function.

If I guess correctly what you try to do, perhaps this version works:

1.     int count = 0;
2.     int[] modelType = { LINES, POINTS, TRIANGLES };
3.    
4.     void keyPressed() {
5.       model.shapeMode(modelType[count]);
6.       noStroke();
7.       count++;
8.       count = count % modelType.length; // Ensure we cycle in the bounds of the array
   
9.     }