General repro in an arbitrary TreeView:

1. Create an empty project
2. Add attached file SimpleTreeView.cs to that project, under the Asset folder
3. Open the TreeView in menu "TreeView Examples/Simple Tree Window"
4. Select an item in the tree view
5. Do CTRL + left mouse click on the item

Expected result:

The item should be unselected

Observed result: 

The item is still selected

Repro in animation window:
1. Open the project “UnityTimelineAnimatorBugReproduce”
2. Open the Animation window (Window → Animation → Animation)
3. Select “Cubes” GameObject
4. In the Animation window select any animation with CTRL + mouse 1
5. Try to unselect the same animation with CTRL + mouse 1

Expected result: Animation is unselected
Actual result: Animation is not unselected

Reproducible with: 2021.2.0a12, 2021.3.5f1, 2022.1.7f1, 2022.2.0a17, 2023.1.0a2
Not reproducible with: 2020.3.36f1, 2021.2.0a11

Reproduced on: Windows 10
Not reproduced on: macOS Monterey 12.4 (Intel)

Notes:
· Same issue in the Timeline window