It's definitely not the first two points, I promise I know how to bypass them xD !
The itch app (I have to say I had no idea it even existed) works. It's a pain since when you decide to click on launch in the app it doesn't work, you have to actually go to the place where you downloaded the game, to click on the icon of the game and then for like 15 times click on the "accept to authorize the game to acceed to...." place where you decided to put the game. Then it finally launch !!!
I'm tired ah, ah, ah. I hope it can help people facing the same problem.
I'll try the demo 1st August on itch.io, on the itch app and on Steam and tell which one is better. I did not try Steam this time but it seems easier than the itch app (not having to click 15 times on an authorization). But I'll try and tell you later !