How to reproduce:
1. Open the user's attached project
2. Open 'SampleScene'
3. Select Tools > ProBuilder > ProBuilder Window
4. Select the Cube object with the Object Selection tool
5. Observe the ProBuilder window

Expected result: The Freeze Transform, Mirror Objects, Flip Normals, Center Pivot, Set Collider options are not greyed out
Actual result: The Freeze Transform, Mirror Objects, Flip Normals, Center Pivot, Set Collider options are greyed out

Reproducible with: ProBuilder 5.0.0-pre.7 (2019.4.19f1, 2020.2.3f1, 2021.1.0b4, 2021.2.0a3)
Not reproducible with: ProBuilder 4.5.0 (2018.4.31f1, 2019.4.19f1, 2020.2.3f1, 2021.1.0b4, 2021.2.0a3)
Cannot test with: ProBuilder 5.0.0-pre.7 (2018.4.31f1) (the package version is not supported)

Notes:
- The issue doesn't reproduce with the Edge, Vertex, and Face selection tools