A very neat and unique idea! The muted color palette is quite pleasant on the eyes, but some elements like the checkpoint flag and the one-way fences(?) are very hard to see against the background. I think the flag should be a very bright color, considering the entire gameplay kinda revolves around it.
The timing for the shift-jump is so tight that it basically feels random. I think the game would flow better if every single obstacle didn't require shift-jumping, since your basic jump is essentially useless without the shift ability, and the shift ability kinda ends up acting like a very cumbersome double-jump. I also wish there were "real" checkpoints, so that every softlock didn't reset you all the way to the beginning.
Unfortunately, my brain was too small to figure out how to get the very first ice cream, or how to get back out of the room behind the horizontal moving wall. So, I sadly gave up after 3 ice creams. That said, the idea of setting your own checkpoints definitely has potential!