I was able to test the Spotify Blends feature out with two friends. It seems that they just add music which you may both have in a playlist or your liked songs! :
Discover and Listen to Music With Even More Friends and Family—Plus Some of Your Favorite Artists—With Spotify's Newest Blend Update — Spotify
How to Use Spotify Blend to Make a Playlist
Top 8 Ways to Fix Spotify Blend Not Working on Android and iPhone - Guiding Tech
Spotify - Think you really know someone? Invite them to... | Facebook
:upscale()/2021/12/09/836/n/1922507/tmp_l3sQDj_e6a821d236bbf11f_PR_2021_TopSong-2048x1152.jpeg "What Is Spotify Blend? Mix Spotify Wrapped Playlists & More | POPSUGAR Tech")
What Is Spotify Blend? Mix Spotify Wrapped Playlists & More | POPSUGAR Tech
Spotify Blend calcule votre compatibilité musicale avec vos potes
Spotify rolls out Blend playlists that combines the listening tastes of two users | TechSpot
Spotify Blend - new features, new ways to share music with your friends - PUSH.fm
Spotify Blend playlists let you co-create mixtapes with your favorite artists | TechRadar
How, and why, to create a Spotify blend playlist | Mashable
Spotify, présentation de Blend - Vidéo Dailymotion
Spotify Blend Lets You Combine Playlists with BTS, or Dad's Book Club - CNET
Spotify blend rolling out in beta allowing the creation of playlists for two by matching your listening history
How to create Blend playlists on Spotify - YouTube
A Look Behind Blend: The Personalized Playlist for You…and You - Spotify Engineering : Spotify Engineering
How to Use Spotify Blend to Create Unique Playlists with Your Friends and Family
How to create Blend playlists on Spotify - YouTube
Spotify Blend: How to Make a Blend on Spotify
Here's how to use Spotify Blend to make and share playlists with others | Tom's Guide
Spotify Blend creates a joint playlist with friends, here's how to use it
Spotify updates Blend feature to create two new playlists based on friends and artists - 9to5Mac
How Spotify's Newest Personalized Experience, Blend, Creates a Playlist for You and Your Bestie — Spotify
