Neon White's Next Fest demo has a lot of notable elements to it that differ from the final game.
Amongst these, possibly the most immediately recognisable change is the music. Neon White has great music but not only does the demo use earlier versions of it, the demo also has some completely different tracks not present in the final game.
I'd normally wrote a proper post about this but I've already spent several hours cataloguing it all on TCRF, so if you're curious, check there: https://tcrf.net/Proto:Neon_White