Hey @matteomulas_ and welcome to the Community.
Hope you're doing great!
Spotify recently pushed an update to the Spotify users which changes the Your Library UI and the way it works. Your saved songs which were in the folder called Songs before now can be found in Favorite Songs playlist, the one with the white heart in a purple background.
Check this Spotify Answer to learn more about the changes to Your Library.
They're always testing and launching improvements and new features. However, if you don't like the new look, please head over to this idea and add your +VOTE. You can always add your own input in the comments there as well 🙂
If you'd like more info on how the Ideas Exchange works, check more here.
and following for any futur status updates.
Hope it helps 🙂