Thank you for your post.
The open windows is a function of Windows. If you have three Chrome windows open, switch to another application, and click on the Task Bar to return to Chrome, you have to select the Chrome window you want to view. The same applies to FileMaker Pro and any other application.
If I return to FileMaker Pro and select a window, pulling down the Window menu and selecting "Bring All to Front" brings back all the other FileMaker Pro windows to the foreground. That is, if I close the topmost FileMaker Pro window, another FileMaker Pro window appears. If this is not working for you, let me know the exact steps you take so I can reproduce the issue.
TSGal: While I agree with you that the windows coming to the front is essentially a default function of Windows, a browser is a collection of totally separate tabs and windows that are each completely independent from one another. FileMaker windows usually all work together as as single solution. Even if there is a Windows default to bring forward only one window, I have to believe there is some kind of trigger that FM engineers can use to bring forward the others automatically.
As for "Bring All to Front", I've just tested again and I now see my mistake. In my tests the other day, as in my initial test today, I had minimized the extra windows. Bringing "all to front" apparently does not restore minimized windows. But if I have all the windows showing, then go to another app, then come back to a FM window and select "Bring All to Front"...that DOES work. That's a start for me.