In Forms 18.104.22.168, WHEN-MOUSE-CLICK fires on both left and right mouse click. However, as mentioned you will not be able to detect which button was pressed due to the bug I mentioned. So in order to detect which mouse button is clicked you will need to patch to 22.214.171.124 then request a courtesy patch for bug 6029080. Once the fix for 6029080 has been applied, you will be able to use my code example to detect which button was pressed.
As I mentioned, you should start by installing 126.96.36.199. It has nothing to do with the issue, but I would also recommend installing WLS 10.3.6. The patch Support provides likely will only be made available for 188.8.131.52 and not 184.108.40.206, unless development is willing to make an exception.