I took a look at my truck to see what I could find.
Looking under the glove box, above the passenger foot area, just behind the heat outlet vent, I can see what appears to be a port going through the firewall.
Looking from inside of the engine compartment, on the right side, about in this same area with some rough measurements, this port seems to match up with that looks like the open drain. This is the same drain I asked my dealer about and was told "it's not a drain, don't touch that".
After the truck is warmed up, if I go for a drive, then stop somewhere for 20 or 30 minutes, then come out and start the truck, I still see condensation start on the inside of the windshield for about 20 seconds, before it dissipates. I also have a faint odor of musty / mold. So there is moisture coming from somewhere, so I want to check the A condensate drain(s).