Closing loading SplashScreen for one Unity instance closes for all other instances

Note: This affects all progress bars in Unity, not only the launch screen.

How to reproduce:
1. Open any project
2. Open any other project
3. While the second project is loading, close the first one
4. Observe the second project’s Launch Screen

Expected result: The Launch Screen stays open
Actual result: The Launch Screen disappears and is transferred to background processes

Reproducible in: 6000.2.0a9, 6000.2.8f1, 6000.3.0b8, 6000.4.0a3
Not reproducible in: 6000.0.60f1, 6000.2.0a8

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: macOS 15.7 (M4 Max)

Notes:

• In 6000.3.0b8, and likely in the 6000.4 stream, sometimes the Launch Screen does not open at all, and loads up in the background (comes to the foreground when the Editor opens)
• Only reproduces if both projects have their Launch Screens (or the editor of the first project) in the foreground
• The second project (the one that hasn’t been closed) will still open after the bug occurs