Hi! First off: love the demo. The animations are gorgeous, and I love details like how there's a special jump animation for jumping out of a roll. It creates a great sense of fluidity to the movement.
I come from a background of speedrunning - particularly Ori, Hollow Knight, and Celeste - so my feedback will probably reflect a lot on those games. I don't mean to be arrogant enough to say I know what the game "should" be, and I assume you've thought of these things yourself, but I thought it would be worthwhile to say anyway.
The controls are extremely tight, but it's possible to have an Attack input eaten. If you press Attack twice, you'll start doing a combo, but if you delay it to the end of the animation of an Attack, you can press Attack and have nothing happen. It's just before you go back to an idle stance. It felt a little off.
It also feels a bit strange that Dashing off walls doesn't give you your Dash back like in Ori and Hollow Knight, but that's probably just cuz I'm very used to those games.
I know it's a very early demo, but, just in case it's not planned, a small idle animation would help I think. There's so much gorgeous motion everywhere else for the protagonist that waiting on the platforms felt a bit strange.
Only other minor things I'd say are that the sound for actually killing an enemy is a bit anticlimactic. I also got stuck on the arrow puzzle thing, but I see others commented that they loved the tutorial for it, so it's entirely possible I just missed that.
I want to reiterate that I really love how the game feels. It's very refreshing having a Metroidvania that frontloads so much fun movement (though I don't know if that's your plan for the final game of course), and chaining Dash Jumps together is real nice. The level design also seemed strong, with a good amount of hidden collectibles. The line of progression also had me consider multiple pathways, which I always enjoy.
Anyway, sorry for the incredibly long comment. I'm really excited to see more from this game!