@Shawn B Do you know how to place the newly opened window at x20, y20 and also size the window like 500 wide 400 high, using XOJO.
It may be stating the obvious, but for Xojo application windows you set the size and placement via properties of that window, such as Width, Height, Top, Left. The problem here is you are wanting to adjust a window that is NOT part of the Xojo application. In order to do that, you need to perform platform specific calls to the OS to modify another application's window. Under most circumstances, it is not considered prudent to modify windows outside your own application. I get where you are coming from in this scenario though, since your app is the one opening these windows.
The general way to control other app's windows is via the Declare statement. A caveat here is that it not only depends on which platform you are running, but also will depend on 32-bit or 64-bit versions. You don't mention here what you need to target, and you put this thread in the General forum section. So I presume you are looking for cross-platforms ways of doing this.
Over the years, some users have created things to help use declares for a given environment. Probably the most widely used of these can be found with forums searches for "MacOSLib" or "Windows Functionality Suite"
But these originated before you had to also worry about 64-bit builds, so they are outdated. For more info, see threads like this and this . But these should also show up in any forum searches you do for the names I gave above.
Note that in your case you don't need everything these extensions have to offer, so you can cherry pick out just the parts you need and create 64-bit versions of only those declares.