There are two possibilities:
- You have bit depth enhancements enabled. You can disable them in HDR mode tab.
- The game was running in fullscreen exclusive and now is running borderless windowed with flip mode. You can change the flip mode checkbox in SpecialK settings.
Fullscreen exclusive games can use HDR10 metadata and/o PQ HDR mode rather than scRGB. This sometimes looks different to very different in games.
For example, see Mass Effect Legendary Edition in HDR mode. It is naturally rendered in PQ, but won’t use that mode unless it’s in fullscreen exclusive, instead converting back to scRGB, which will change primary handling as well as brightness and color peaks as metadata is not sent to the screen.
The metadata not being applied even when fullscreen optimization is active is probably an nVidia thing.
PQ mode (10-bit) is possible to force in SpecialK configuration file and should work still with borderless windowed, though not necessarily the same as in fullscreen exclusive. (Option Use10BitSwapChain=true)
Most games do not use PQ mode for output or if forced, do not detect it correctly.