I installed with the itch-app, and that worked fine to start.
How this game turned out to be 300mb is interesting. Did you use the context menu item called "make local"? I've been owned by that in previous jam, where a textured mesh was turned into text in the .tscn and that .tscn became 100 mb big. So I kind of think that button should come with a big fat warning on it.
The animations of the char were really funny I think, good work there!
I had a problem with climbing over a ledge (?) when climbing in side view. The character just started falling when reaching the top.
It would have been cool if the nice thematically correct cursor could be used for something in game too perhaps, or otherwise be hidden so that I was not distracted while playing.
Some ingame tutorial or how to play would have been good too, because I had to read on the itch page about ctrl for starting climbing.
Hope you had fun making it and complete it afterwards (or start a new project, that's often how I do it =)