Whilst this question does not appear to be related to Sonos, I understand you will only be able to ‘browse’ your own music library (if that’s what you are referring to here?) after you have uploaded your tracks to it.

See this YTM link:

https://support.google.com/youtubemusic/answer/9716522

Was typing question too fast.  I have Sonos in my home.  I added you tube music choice to the list of apps one can use w the Sonos app.   In addition to the you tube music I have Amazon music and several other apps where I can Open the Sonos app and search for music and the app goes to one or more of the other apps and finds a song and I play It.  I browse Amazon music for whichever song it comes up.  Issue is when in the Sonos app and want to search for a song in yt music it says no selections are available.    Hope this clears up my original question.  

Do you have a free YouTube Music account or a premium account? If you only have the free account, you need to upload your music to your YouTube Music library. See the link posted by @Ken_Griffiths for instructions.