Would be nice to have a direct "add to playlist button" next to the add to favorites button (on the now playing screen). Or maybe long pressing the favorite button is opening a "add to playlist" menu.
@Yoelilev is suggesting that the button to add a song to a playlist be moved out of the 3 dot menu so it’s easier to access. If it’s a design issue, then tapping and holding on the favourite track button should open the add track to playlist menu. I would not remove the add to playlist menu item because even though there is a direct favourite track button, it is still there in the menu (which is good for users who don't know what the heart icon means). There is the issue of educating users but a simple balloon/tooltip (WinUI over on Windows 10 calls it TeachingTip) the first time a user opens the now playing screen would suffice! Here’s a link: https://medium.com/swlh/a-lightweight-tooltip-popup-for-android-ef9484a992d7
Deezer can grow a lot more when users share their playlists ;)