How to reproduce:

1. Open the project “IN-64237_HDRP_Multi-Camera_UI_HDR_Tests“
2. Open “Test B“ scene
3. Drag the Game window to a -4K 10-bit- HDR-capable display and maximize it.
4. Enter Play mode
5. Observe Game window UI text "HDR is OFF" and press "H" key to enable it
6. Observe the Game window

Expected result: Game window is displayed properly with the UI
Actual result: Game window turns black

Reproducible with: -2021.3.34f1,- 2022.1.0a16, 2022.3.17f1, 2023.2.6f1, 2023.3.0b2
Not Reproducible with 2022.1.0a15

Reproducible on: Windows 11 Pro (23H2), Mac M1 Mini, Macbook Pro 2018

Note: a workaround is to Enable the “S Camera” and disable the “Black BG” (child of “Canvas”).
Note: Does not actually require 10-bit 4k monitor, just an HDR capable monitor.