How to reproduce:
1. Create a new Unity project
2. In the Hierarchy, create any GameObject
3. Open the Animation window (Window -> Animation -> Animation)
4. With the GameObject selected, click "Create" in the Animation window
5. Right-click anywhere on the Timeline -> Add Animation Event
6. Select the Animation Event, and click the "?" button in the Inspector

Expected results: The documentation opens
Actual results: The documentation is missing

Reproducible with: 6000.0.65f1, 6000.3.3f1, 6000.4.0b3, 6000.5.0a3

Reproducible on: Ubuntu 24, macOS Tahoe 26
Not reproducible on: No other environment tested