How to reproduce:
1. Open the “Timeline2023_3_0b3” project
2. In the Project window open the “Assets/Content/New Timeline.playable” Timeline Asset
3. In the Timeline window select the “New Animation” Track
4. In the Inspector window select one of the curve fields
5. Observe the Inspector window

How to reproduce in new project:
1. Create a new project with any template
2. Create a new Animation Asset (Assets > Create > Animation)
3. Create a new Timeline Asset (Assets > Create > Timeline)
4. Open the newly created Timeline Asset
5. In the Timeline window add the newly created Animation Asset
6. Select the “New Animation” Track
7. In the Inspector window select one of the curve fields
8. Observe the Inspector window

Expected result: The Curve Editor window is shown
Actual result: The Curve Editor window is not shown

Reproduced with: 1.8.5 (2023.2.0a19), 1.8.6 (2023.2.11f1, 2023.3.0b8)
Not reproduced with: 1.8.5 (2023.2.0a18), 1.8.6 (2021.3.35f1, 2022.3.20f1)
Could not test with: 1.8.6 (2023.2.0a18, 2023.2.0a19) (“Timeline” Package throws multiple compilation errors)

Reproduced on: Windows 11
Not reproduced on: No other environment tested

Notes:
1. The regressed version is not in the package version, but the Editor version → The FAV is 2023.2.0a19
2. Not reproducible in Particle Curve Editor