Thanks for taking the time to play through the game and leave us your feedback! We taking a lot of notes from the people who have played and we agree an in-game tutorial and a handful of QoL updates are in order.
Looking into that black screen bug this morning, I am happy to inform you that you indeed did beat the base game! After beating the pre-determined levels provided, there is a silent hand-off to Infinite mode. And we've found the bug lies in that handoff.
So in addition to the note to make the win condition more apparent in a future update, congrats on beating the demo and proving your craftiness as an alchemist of light and shadow!