Steps to reproduce:

1. Create a new Project using the Universal 3D template on the 6000.4.0b10 Editor version
2. Quit the Editor
3. Change the Editor version for the Project in Unity Hub to 6000.5.0a7
4. Click the "Open with 6000.5.0a7" button
5. Click the "Change version" button on the popup window
6. Click the "Quit" button in the Project Upgrade Required Splash Screen popup
7. Change the Editor version for the Project in Unity Hub back to 6000.4.0b10
8. Click the "Open with 6000.4.0b10" button
9. Observe the Splash Screen popup

Actual results: The Project Library was corrupted even after pressing the "Quit" button to cancel the project upgrade

Expected results: The Project Library should not get corrupted or any changes to the Project made since the upgrade was cancelled

Reproducible with versions: 6000.0.68f1, 6000.3.10f1, 6000.4.0b10, 6000.5.0a7

Tested on (OS): MacOS Silicon Tahoe 26.2

Notes:

• Seems to reproduce with all Editor versions