Running chromium on say, a raspberry pi 3 model A in kiosk mode kicks out a warning dialog that you can't prevent.

I found out it, with some help, it's the /usr/bin/chromium-browser script that does it.

Does this script come from DietPi? Or is it from the RPi-Distro debian script? I can see it's the same.

Either way I'd recommend gouging out this warning because, well, not only does it run reasonably well depending on your purposes, but it shouldn't have interstitial dialogs when booting into kiosk mode.