Steps to reproduce:
1. Create a giant unique desktop with NVidia or AMD built-in tools (4500x720px)
2. Open Unity
3. Detach the Game View from the editor
4. Try to resize the Game View
5. Observe, that it is not possible to resize over 4014 pixels

Expected result: Game View should be resized
Actual result: Not possible to resize over 4014 pixels

Note:
With 4500x1080 you will be able to resize over 5000

Reproduced with: 5.5.0a1, 5.5.0f3, 5.6.0a6
Not reproduced with: 5.3.6p8, 5.4.3p3
Regression introduced in 5.5.0a1