Question AddScore by PlayerId ?

Hi,

I am using the Xsolla authentication solution for various reasons, but unfortunately it means I have problems using a lot of Unity Services which rely on Unity authentication. Of course I can use the anonymous login, but when I add a score in the leaderboards it will be connected to the device the user used for submitting the score, which is fine in most cases until the user changes the device.
I saw that it is possible to receive user scores by PlayerIds (although I am not sure how this Id is created and how I get it for other players like friends), because you don't submit a PlayerId when adding a score, so I guess it will be created by the authentication system.
If I would be able to add a score by PlayerId and receive scores by PlayerId it would help a lot because I can use my Xsolla Ids to get the scores for a certain player when using anonymous login. Anything like this coming? I saw another solution which allows exactly this, but I would prefer sticking to Unity for leaderboards.

Thanks and best regards,
Marco