Suedkiez
(Just a fellow user like you)
2
You can only 
tracks that are in the library, so yeah you have to add it to the library first if it isn’t, like it happens e.g. on Roon Radio.
It’s one of the many things in Roon where the in-library / not-in-library difference leads to some complications.
See this from 2019 which is still valid: