Copying this over from Steam since I only checked out the demo just now, and i don't know if you are reading posts over there. Sorry, I can't spoiler stuff on Itch:
In short, nearing what I believe is the end of the demo, the entry to the cave that has Metro can bug out. Specifically, the alternative entrance near Crater.
This is performed after the nuke goes off and you go in the entrance before talking with all of the town leaders. After the sister character calls you out to talk to the remaining town leaders, disabling the map transition, it will never re-enable, even after closing and restarting the game program.
The first other map transition point near Oil Extraction still functions, but ice mechanics makes that route difficult if not impossible if you have a heavy load.