How can I open a program on a specific monitor on a RPi4

I am trying to open sndpeek, a program powered by GLUT, on my second monitor plugged into HDMI-2 port on a Rpi4, but I get an error that
freeglut (sndpeek/sndpeek): failed to open display ':0.1'

I have gone back and forth with ChatGPT trying to solve this. All the necessary permissions are in place, I am at a loss here.

(I am building a robot head that hes screens for eyes and mouth, two programs must be run at startup, one for the eyes, and sndpeek for the oscilloscope mouth.)

Can you open any program on :0.1? Does xdpyinfo indicate that the display :0 has two screens?