So the free demo has features...
That the paid version has not.
Also intentionally you sell the 3 versions behind game, on 20 dollars.
The demo has the purpose to show some features the game will have, it has a sneak peek of features that have not fully developed yet and we haven't put into a public version because they are still work in progress.
The Itch version is the most up to date public version we have. It is only 3 versions behind our developer closed beta builds which are not ready for publishing yet.