How do I exclude specific local files from my library?

[4q67tfsi9e04gjk]

I've been using Spotify on my phone. I told it where my local files are, to save on downloading them again. But I'm using my Spotify library for only the songs I really, really like rather than all the misc **bleep** I've accumulated over the years. You know, not-so-great tracks on an album you bought?

Anyway, on the mobile app, for all songs in my library - even ones from the local files - I can uncheck the checkmark in the player to remove a song from my Spotify library. But I can't see that option in the Desktop program.

In the desktop program, the green checkmark appears for non-local tracks, but not for local tracks. In the mobile app, it appears for both.

Am I missing something? Is it possible to exclude ("unlike"?) local tracks?