How to reproduce:
1. Create a new Unity project
2. Install the MLAPI package (you can follow this tutorial https://docs-multiplayer.unity3d.com/docs/migration/install/index.html)
3. In the Hierarchy right-click and go 3D Object -> Cube
4. Select the "Cube" GameObject and in its Inspector click Add Component
5. Search for "NetworkManger" and click on it
6. In the NetworkManager component click on the "Open Reference for NetworkManager" button

Expected results: The documentation page that gets opened exists
Actual results: The opened documentation page doesn't exist

Reproducible with: 2019.4.26f1, 2020.3.11f1, 2021.1.9f1, 2021.2.0a19 (0.1.0)
Could not test with: 2018.4.35f1 (MLAPI package not available)

Note:
- In version 2020.3.11f1 the MonoBehaviour documentation page is opened
- In step 5 "NetworkManager" was used as an example, the issue reproduces with all possible MLAPI components