ah you've probably already seen but steam only has the prologue up at the moment, no legacy demo. by your picture everything looks to be in order, but just in case can i see inside the txt folder?
thank you, it looks fine. From your screenshot, it looks like it's still in the zip file, so i thought maybe if you moved it into a folder on your computer it might work... but I tried it for myself and it seems to work fine even if run from the zip file.
i managed to get that exact code error by deleting one of those txt files, so i really can't think of any other reason it might be giving that error, especially on a fresh download. i'm so sorry 😔