Custom Blends camera selection dropdown doesn't work

Reproduction Steps:
1. Open/create a project and add Cinemachine package
2. In a new scene GameObject > Cinemachine > Cinemachine Camera
3. Asset > Create > Cinemachine > BlenderSettings
4. Select the Main Camera and scroll down to Cinemachine Brain component
5. Drag and drop BlenderSettings into Custom Blends Asset field and expand it
6. Press the selection arrow in the From setting and select ANY CAMERA
7. Press the selection arrow in the To setting

Expected results: All possible cameras dropdown selection appears
Actual results: No selection box appears

Reproducible with: 3.0.0-pre.5, 3.0.0-pre.7 (2022.3.4f1, 2023.2.0a21)
Not reproducible with: 2.9.7, 3.0.0-pre.4 (2022.3.4f1, 2023.2.0a21)