Save to file/Open popup window appears behind the UI Builder window when the Open/Save File button is pressed on linux

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Create a UI Document asset (Assets > Create > UI Toolkit > UI Document)
3. Double click the new UI Document asset to open it in the UI Builder window
4. Click the "File" button at the top of the Viewport
5. Select either "Open..." or "Save as..." options
6. Observe the Editor

Actual results: The Open/Save popup window appears behind the UI Builder window

Expected results: The Open/Save popup window appears on top of the UI Builder window

Reproducible with versions: 6000.3.0a2, 6000.3.0a4

Not reproducible with versions: 6000.0.54f1, 6000.1.14f1, 6000.2.0b13, 6000.3.0a1

Tested on (OS): Ubuntu 24.04

Notes:

• Does not reproduce on macOS Silicon Sequoia 15.5