How to reproduce:
1. Create a new Unity Project
2. In Toolbar settings, go to Unity Editor > Quality and add the Quality dropdown menu
3. Go to Project Settings > Quality
4. Add 2 new Quality Levels (Level 1 and Level 2 will be created by default)
5. In the Settings window select the Level 2 Quality Level
6. Delete the Level 1 Quality Level
7. Observe the Quality Level displayed in the Quality dropdown menu in the Toolbar

Actual result: Level 1 Quality Level is displayed even though it was deleted
Expected result: Level 2 Quality Level is displayed

Reproducible with: 6000.3.0a5(f9a1fab5607a), 6000.3.7f1, 6000.4.0b7, 6000.5.0a6
Could not test with: 2023.1.0a1, 6000.0.65f1, 6000.3.0a4 (customizable toolbar was introduced in 6000.3.0a5)

Reproducible on: Windows 11, Windows 10 (by user)
Not reproducible on: No other environments tested