Unfortunately seem to have encountered a bug on my end where the puzzle pieces in the second major area never properly get collected, holding back progression :(
Oh no! I'm so sorry! You are not the first to have some issues, I think it's due to saving/loading.
Sadly this is something really hard to debug since on my end everything is working properly. I'll see if I can find the problem and also maybe release an update where there's a way to reset the game's progress since now you are locked.