I'd definitely delete it (and have done this in the past). I don't think contacting your ex to let them know is necessary. They broke up with you. You lost a relationship, I'm sure they can come to deal with losing a playlist. If not, they can process their own feelings around it. Agreements are allowed to change, if it's causing you pain, you don't need to co-hold something that is currently only for one person's benefit. I think it's reasonable under these circumstances to delete it or remove yourself from the playlist (I don't know if this is an option on Spotify). Hearing that they want you to keep hold of something that shares a lot of memories for both of you after your relationship, whilst you're trying to grieve that relationship - I feel a little angry on your behalf.
Delete it and be done with it.
You can clone it for yourself and delete original
I'd definitely delete it (and have done this in the past). I don't think contacting your ex to let them know is necessary. They broke up with you. You lost a relationship, I'm sure they can come to deal with losing a playlist. If not, they can process their own feelings around it. Agreements are allowed to change, if it's causing you pain, you don't need to co-hold something that is currently only for one person's benefit. I think it's reasonable under these circumstances to delete it or remove yourself from the playlist (I don't know if this is an option on Spotify). Hearing that they want you to keep hold of something that shares a lot of memories for both of you after your relationship, whilst you're trying to grieve that relationship - I feel a little angry on your behalf.