Reproduction steps:
1. Create a new project
2. Create Animation Controller and Animation Clip in the Project window (Create > Animation)
3. Window > Animation > Animator
4. Right-click in the Animator window and select Create State > Empty twice to create two States
5. Right-click on one of the States, select Make Transition option and connect it to another State
6. Attach Animation Clip to both of the States in the Inspector
7. Select transition between two States and select “Other…”in the Preview Model dropdown
8. Select any of the GameObjects in the “Select Game Object” window
9. Select “Other…”in the Preview Model dropdown again
Actual result: “Select Game Object” window doesn’t appear
Expected result: “Select Game Object” window appears
Reproducible with: 6000.0.0f1, 6000.0.81f1, 6000.3.21f1, 6000.5.7f1, 6000.6.0b7, 6000.7.0a4
Reproduced on: macOS Tahoe 26.5 (M4), Ubuntu 24.04