@Paul
500mbar (= 500hPa) thickness is available as isolines (Geopotential height isolines) but unfortunately not as a chart.
Here shown with Wind layer and Temperature layer

6A99E33B-03F0-4E9F-A270-385580ABA7B8.jpeg

Press More layers... in the right Menu and select Geopot. height. Then adjust the altitude slider at 500hPa

Capture d’écran 2020-05-14 à 10.48.00.png