You can fix this by editing your save file manually: it's in %AppData%\LocalLow\The Prismatic Forge\Isekaidle\saves and you need to replace both instances of NaN with 0. This will let you see the rest of the demo, although there are still issues around queueing.
yes, there were 4 instances. i fixed them. then eventually wound up with dozens of axes and handsaws and on repairing the carpenter station was no longer able to access it, e.g. could never turn the logs into lumber to proceed
had to alter the amount of crushed rock (135->200) so that i could do the floor repair as almost no rock drops via the lowest tier after a while
