When starting the chromium browser under X11 on the Desktop image the display initially loads a blank screen (on the attached monitor) and it takes about 15 seconds (on my Pi5) before the PicoChess page appears. Sometimes it will stay as a blank page until you can perform a refresh of the browser (F5 on an attached keyboard or 'DISPLAY=:0 xdotool key F5' via ssh).
To fix this, edit the kiosk.sh file in the pi home folder and add the flag '--password-store=basic' to the following line:
/usr/bin/chromium-browser --enable-features=OverlayScrollbar --password-store=basic --display=:0 --noerrdialogs --disable-infobars --kiosk http://127.0.0.1 &
Save and reboot. I'll add the fix to the images the next time I update them.
Randy