Reproduction steps:
1. Open the attached project "Case_1405619.zip" and load Scene "Main"
2. Enter Play Mode
3. In the project window select "Assets/TestCubemap.renderTexture" and observe its preview
Expected result: UI is visible in the Cubemap
Actual result: UI is missing from the Cubemap
Reproducible with: 2019.4.37f1, 2020.3.32f1, 2021.2.18f1, 2022.1.0b14, 2022.2.0a9