Reproduction steps:
1. Open the attached “IN-48797 HDR Splashscreen.zip“ project
2. Make sure that the project is running in the Direct3D12 API (for testing HDR in the Editor)
3. In the Player settings, in “Other Settings”, enable and disable “Allow HDR Display Output”
4. Observe the difference in the brightness/colours of the Editor

Expected result: The colours and brightness of the Editor are identical to the SDR mode
Actual result: The Editor becomes darker

Reproducible with: 2021.3.29f1, 2022.3.7f1, 2023.1.9f1, 2023.2.0b5 (DX12)

Reproduced on: Windows 11 Pro 22H2, macOS 14.0 Darwin 23.0.0 (by the user)
Not reproduced on: No other environment tested

Notes:
- In the user’s case, they experienced overly saturated colours in the Editor instead of darker ones (see user-attached “Screen Recording 2023-07-23 at 13.49.12.mov” video)
- Reproducible in a new project
- Could not test with Vulkan API (Swap chain with supported HDR formats not found. Using supported SDR swap chain format)
- Monitors used: Alienware m15 R3 internal OLED HDR display and Samsung Odyssey G9 in HDR mode