How to reproduce:
1. Create a new empty Game Object
2. Assign a Mesh Filter component
3. Click on the object picker icon in the Mesh Filter Component

Expected result: In the Select Window you can see the default meshes (cube, sphere, etc.)
Actual result: The Select Window is empty

Reproducible with: 2021.1.0a1, 2021.1.0b6, 2021.2.0a1, 2021.2.0a3
Not reproducible with: 2018.4.30f1, 2019.4.19f1, 2020.2.4f1, 2021.1.0b7, 2021.2.0a4

Notes:
1. Mesh and Texture assignments don't work (gif attached)
2. Volume profiles seem to show only when their names are typed out, but all asset types are shown (gif attached)