Hello are you using a CRT screen? you can try to edit your recalbox.conf like that :

## If you use rice core, set mode 480p as below n64.core=rice n64.videomode=CEA 2 HDMI

then inside your /recalbox/configs/mupen64/mupen64plus.cfg add your screen resolution here :

[Video-General] # Use fullscreen mode if True, or windowed mode if False Fullscreen = False # Width of output window or fullscreen width ScreenWidth = 1280 # Height of output window or fullscreen height ScreenHeight = 720 # If true, activate the SDL_GL_SWAP_CONTROL attribute VerticalSync = False

In this example, it is setup for a HD resolution of 720p.