Here's a youtube where I explain this: https://www.youtube.com/watch?v=SCVrAUXXugg
Fullscreen games I run with Freesync enabled become dimmer than they should be, but only when in focus. If I click out of it it gets brighter, and if I click in, after about a second it gets dim again.
This only happens with Fullscreen games, and if I turn off free sync it stops happening.
6800XT 4k 144Hz HDR if it matters.