No "Add track to playlist" button

[palindrome]

I'm trying to make a collaborative playlist with my friends.

Not only am I not able to view her playlist unless she shares the link, even if it's set to public, but I'm not able to add any songs to it.

I've had Spotify for two days and I've been making playlists by searching the track, then adding it to a playlist.

But my friend has a big "Add track to playlist" button under the playlist's name.

I have never seen that option in my app, not even in my desktop version.

Why is it not in my app?

In the attachment you can see what button I'm talking about (it's in italian)