One option is to use the Split option under the Tables menu to make separate columns for A and B (split column EH, split by Platform). The, you would use two different lines in graph builder. Build your chart but add both columns to the y axis in graph builder. Right click in the chart area and choose Add > Line. Now in the area where you chose Min you will see two different lines, choose min for one and max for the other. You should see four lines on the chart, the min of A and B, and the max of A and B. Now under 'Variables' below where you picked Min, deselect B from the Max, and deselect A from Min.
Another option is to build the graph with lines for both min and max for all levels of Platform and just hide the lines you don't want. In the chart you showed in your post, add a second line the same way you did in the previous option and change one line to min and one to max. Now go to legend settings, check the boxes to display all four labels, then work out which lines are the min and max for each one and change their transparency to 0. Now go back to legend settings and hide the transparent labels.
Here is a script that should recreate these two charts: