Two fullscreen tkinter windows on separate monitors on Raspbery Pi 4
You have to offset the second window to the right by the width of the first display (The X system puts the display on the HDMI0 port down first, then puts the display from HDMI1 to the right).geometry lets you make sure they don't overlap and then fullscreen works as expected.
The format of the geometry string is: <width>x<height>+xoffset+yoffset.
root = tkinter.Tk()# specify resolutions of both windowsw0, h0 = 3840, 2160w1, h1 = 1920, 1080# set up window for display on HDMI 0 win0 = tkinter.Toplevel()win0.geometry(f"{w0}x{h0}+0+0")win0.attributes("-fullscreen", True)# set up window for display on HDMI 1 win1 = tkinter.Toplevel()win1.geometry(f"{w1}x{h1}+{w0}+0") # <- the key is shifting right by w0 here win1.attributes("-fullscreen", True)root.withdraw() # hide the empty root window