What does it mean when a guy make a playlist and just added all the songs I've suggested?

That he wants to listen to the music you like. Maybe he likes you. Maybe he thinks you have good taste. Maybe he wants to see if you have good taste.
Well I've made a playlist with the one I'm involved with we both add songs to it that are aspects of our relationship 🤷♂️
Opinion
2Opinion
He likes your taste in music.
Same music taste confirmed!
You have a good taste. He wants to be similar
He likes your taste
In music
Superb Opinion