Windows ((full)) Fullscreen Optimization Disable -

Windows Fullscreen Optimization: Should You Disable It? is a built-in feature designed to give gamers the best of both worlds: the performance of Fullscreen Exclusive (FSE) mode and the convenience of Borderless Windowed mode. While it generally improves the gaming experience by allowing faster alt-tabbing and overlay support, some users find it causes stuttering or input lag in certain titles.

While intended to help, many users disable this feature to resolve specific technical issues: windows fullscreen optimization disable

Demystifying Fullscreen Optimizations - DirectX Developer Blog Windows Fullscreen Optimization: Should You Disable It

Use this to disable the feature for every game on your system. windows fullscreen optimization disable

When a game requests Exclusive Fullscreen and FSO is (the default), the OS performs a sleight of hand: