I finally finished the demo! Really promising! The web build is not that broken (for me it was worse on linux+wine), but I really recommend the downloadable version to enjoy the music, that you can’t here on web (at least for this version).
Spoilers below:
The collectible that’s hidden out of screen, that you need to walljump through a tiny space it’s the only one that feels unfair. The rest are well hidden and feel rewarding to find. The story and the misteries (the red moss/grass, the strange person with the weird language, the eclipse) got me hooked and wanting for more.