How to reproduce:
1. Open attached "Timeline.zip" project and scene "SampleScene"
2. In Hierarchy window, select the Timeline GameObject
3. In Timeline window, Start Recording for the "Cube (Animator)" track
4. In Hierarchy window, select the Cube GameObject
5. In Inspector window, set the "Some Script" component's values to True
6. Observe Timeline window
7. In Inspector window, modify the Cube GameObject's Transform component
8. Observe Timeline window
9. In Inspector window, set the "Some Script" component's values to False
10. Observe Timeline window

Expected result: The script component's value changes can be recorded initially
Actual result: The script component's value changes can only be recorded after a change in the transform component has been recorded initially

Reproducible with: 1.8.6 (2023.2.0b12, 2023.2.1f1, 2023.3.0a15)
Not reproducible with: 1.6.5 (2021.3.32f1), 1.7.6 (2022.3.14f1), 1.8.6 (2023.1.20f1, 2023.2.0b11)

Tested on: Windows 10

Note: After the transform value is recorded initially, even if the recorded value is deleted, the script component's changes can be modified via the Timeline Recorder

Here's how to reproduce the bug with the Animation window:

1- Open the Animation window

2- Click on "Create" to create a new animation clip

3- Click on the record button

4- Select the Cube gameobject

5- In the inspector window, change a value in "Some Script" component

Expected: a keyframe is added in the Animation window

Result: nothing is added to the Animation window

!record.gif!