How to reproduce:
1. Open the attached project's "case_1334450-Project.zip" Scene labeled "SampleScene"
2. In the Game View window, set the resolution to 1024x1024
3. In the Hierarchy, make sure that only the "Base Camera" is enabled
4. Enter the Play Mode
5. Open the Memory Profiler (Window -> Analysis -> Memory Profiler)
6. In the Memory Profiler window, capture a memory snapshot
7. Open the captured memory snapshot
8. Search for "_CameraColorTexture" (right-click the 'Name' column and select 'Match')
9. Note the 'Native Size' (20MB)
10. Exit the Play Mode
11. Enable the "Overlay Camera"
12. Enter the Play Mode again
13. Capture the memory snapshot again
14. Open the captured memory snapshot again
15. Look up the "_CameraColorTexture" plus "_CameraDepthAttachment" Native Size

Expected result: "_CameraColorTexture" Native size with "Base Camera" should be the same as "_CameraColorTexture" + "_CameraDepthAttachment" Native Size when using an Overlay Camera
Actual result: "_CameraColorTexture" + "_CameraDepthAttachment" Native Size when using an Overlay Camera is bigger by 2MB

Reproducible with URP: 7.7.1 (2019.4.29f1), 10.0.0-preview.26 (2020.2.0b12)
Reproducible with Memory Profiler: 0.2.10-preview.1 (2019.4.29f1, 2020.2.0b12)
Not reproducible with URP: 10.1.0 (2020.2.0b12), 10.6.0 (2020.3.17f1), 11.0.0 (2021.1.18f1), 12.0.0 (2021.2.0b9, 2022.1.0a5)
Couldn't test with Memory Profiler: 0.2.10-preview.1 (2020.3.17f1, 2021.1.18f1, 2021.2.0b9, 2022.1.0a5) (Issue is not reproducible with the available URP version)