Reproduction steps:
1. Create a new project
2. Install Multiplayer Play Mode package (Window > Package Management > Package Manager)
3. Wait for the package to finish installing
4. Observe the top Editor toolbar
Actual result: "Default Play Mode" button does not appear in the toolbar
Expected result: "Default Play Mode" button appears in the toolbar
Reproducible with: 3.0.0 (6000.6.0a1, 6000.6.0a7)
Not reproducible with: 1.6.3 (6000.0.76f1), 2.0.2 (6000.5.0b12)
Reproduced on: macOS Tahoe 26.5 (M4), Windows 11
Note: Button appears after forcing a domain reload (e.g. creating a Script)