So I know Itch does actually support that, but I'm pretty sure it wouldn't really save anything since the way Godot exports it is just as 2 big files and then the tiny .dll (and the custom map folder). It would force you to download both the big files anyway since they'd always change with an update, so all that you wouldn't have to download is the dll and the folder, which is like 2% of the size of the game.
I am going to try to reduce the size of the game in general going forward though, I was probably going a bit overkill on the audio quality, the Ch3&4 maps will be a bit more compressed (not too much though, it shouldn't be audibly noticeable). So the Ch3&4 maps will be smaller when they release, and I'll also try to find time to re-export the Ch1&2 maps to use better compression as well.