Euphony.1.0

@baratacichetto: Hello there,
To add a sticky playlist like in the demo you will need to first create a playlist.

For Gutenberg editor first you will need add a Classic Block.
Edit a page => Add New Block => Formatting => Classic Block

After adding Classic Block click on Add Media button => Create Audio Playlist => Select your Audio Files and Click on Create a New Playlist.

Then,
Go to => Appearance => Customize => Theme Options => Sticky Playlist => Enable the section => Select the page where you created the playlist earlier and Publish.

Let me know if this helps you out!
Kind Regards,
Skandha