You can use a combination of
GetForegroundWindow and
SetForegroundWindow function from Windows' user32.dll to ensure that the exe (VI) is always active frontmost while it is running as per below LabVIEW snippet.
Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project.
To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW block.