Use the D3D9Ex API introduced in Windows Vista, instead of normal D3D9.
Defined in SDL_hints.h
#define SDL_HINT_WINDOWS_USE_D3D9EX "SDL_WINDOWS_USE_D3D9EX"
Direct3D 9Ex contains changes to state management that can eliminate device loss errors during scenarios like Alt+Tab or UAC prompts. D3D9Ex may require some changes to your application to cope with the new behavior, so this is disabled by default.
This hint must be set before initializing the video subsystem.
https://docs.microsoft.com/en-us/windows/win32/direct3darticles/direct3d-9ex-improvements
This variable can be set to the following values: