neowin[.]net/news/windows-11-insiders-now-have-optimizations-for-legacy-games-running-in-windowed-mode/
devblogs.microsoft[.]com/directx/demystifying-full-screen-optimizations/
devblogs.microsoft[.]com/directx/updates-in-graphics-and-gaming/
Starting with Windows 10, when Fullscreen Optimizations are enabled, a game doesn't really run in fullscreen mode, but in a borderless window sized to fill the display. Doing so lets Windows perform some tricks to enhance performance. That may be one reason Win10 is judged better for gaming than Win7. It's also why disabling that optimization in an older game's compatibility settings may help. The latest Win11 Insider builds in the Dev channel now allow those same optimizations for games in windowed mode, targeting DX10/DX11 games.
"You can check whether Fullscreen Optimizations are enabled or not by opening the Xbox Game Bar via Win+G. If you are running in Fullscreen Exclusive, then the display brightness may be flicker. If you are in Fullscreen Optimizations, the Xbox Game Bar should pop up as an overlay."
"If you find that you are having trouble with Full Screen Optimizations, such as performance regression or input lag, we have some steps that can be useful. This includes how to disable the feature for any specific game, but also how to provide us with feedback regarding your gaming experience.Below are the instructions on how to disable Fullscreen Optimizations for a game.
Right Click on the Executable File (.exe) and Select Properties
Select the Compatibility Tab
Under Settings – Select “Disable Fullscreen Optimizations”
Click Apply"
For the new windowed mode optimizations:
"Your DX10/DX11 game needs to be running in a Windowed or Borderless-Windowed environment to use this feature.How to Opt In
If you would like to use this feature on games and applications, please follow the instructions below.
Go to Settings
Go to System -> Display -> Graphics
Then go to Default graphics settings
Scroll down to Optimizations for windowed games and turn the setting On.
Restart your game "
"Per-App Opt-OutThese instructions are to help you choose which graphics settings you would like to opt-out of on a specific game or application.
Go to Settings
Go to System -> Display -> Graphics
Select an application and click Options
Select which features you would like to opt-out of
Check the box for Don’t use Optimizations for windowed games
Check the box for Don’t use Auto HDR
Check the option for GPU preference (for devices with more than 1 GPU)
Save the selection
Restart your game"