The maximum usable resolution is currently 1024x768, only 4: 3, not 16: 9. BPM Studio full screen is therefore only possible with 800x600 and 1024x768. At 1280x1028 and higher, the desktop is visible on the left and right.
Alternatively, the resolution of the graphics card can be switched when the program starts. To do this, set "Change resolution at start" in the BPM Studio options (right mouse button).
You can also change the scaling in the advanced graphics card settings. With Nvidia this setting can be found e.g. in the Nvidia Control Panel, under flat screen scaling, change scaling from "no scaling" to "Nvidia scaling". It is best to make this setting only when BPM Studio has been started with the resolution switched.