I opened a new member or sharing playlist (like the family playlist which will not be supported in future). I shared the invitationlink. Now I have a member at my playlist, which came a few days later as the others and I do not know. How can I get rid of this account in our playlist or how can I get in contact to this person to ask who he/she is?
It should be possible for the owner of the playlist to add/remove members to the collaborative playlist, if we understand you correctly and you're talking about a collaborative playlist. That's why we need to know if you're the owner of the playlist. Is that the case? Could you post a link to the playlist so we can check it?
In the meantime you can have a look at this page to find out how to add/remove members to the playlist.
Keep us posted,
Help others find this answer and click "Accept as Solution".
If you appreciate an answer, maybe give it a Like.