It is because most of the laptops have two graphic cards. In case you are using a laptop, you might experience the black screen window. You should also try to "Run as administrator" the OBS Studio.
After restarting your PC, you should try to use OBS and play a game while the Game Mode on Windows is being disabled.Next, restart your PC to make sure the settings have been changed.From the Game Mode section, toggle the feature "Off" to disable the game mode on your Windows PC.Then, search the "Game Mode" option in its search bar.Go to the "Settings" menu by searching it on the "Start" menu, and a new tab will appear afterward.Quick guide to disable Windows 10 game mode: It can also conduct the GPU resources away from OBS, which can cause the viewer to see sluggishness on live streaming. However, some of the streamers reported that it obstructs their broadcast. This feature on Windows 10 was released in 2017, and it is made to improve the process of your PC when playing games. If you have experienced this issue, you should try to disable the Windows 10 Game Mode. There is much potential error that causes this problem with games. It can be a hassle for gamers who are live-streaming their games. Many OBS users say that they experience a black screen while recording gameplay.