Very well made game. Good controls, good puzzle design, clear graphics, and good music. It could have done with some more difficult puzzles at the end. Also, I think it would fit better for the boxes to have simpler physics, rather then using some RigidBody physics, with unpredictable pushing and rotating physics. They felt very slippery, and the odd tumbling made level 12 more annoying then needed. I personally am not a fan of auto jump when holding space. With the platformer tradition of longer presses equals higher jump, I keep space pressed when jumping for all games, meaning I constantly jumped off corners just when reaching them. There were two levels I found confusing. I feel like I cheesed level 9. I only used one grow pellet, to jump around the level on the right. I could not figure out how to get up in the middle, but the jump I did was by far the most difficult one in comparison with the rest of the game. Also, in level 15, it was unclear where the end coin actually was. But overall amazing work, and good luck on any further endeavours.
PS. Two small things. If you have unity WebGL, you should disable the full screen button itch.io provides, since now there are two full-screen buttons, one of which is useless. Also, it seems currently impossible to get from the win screen back to the menu.