I've tried everything that has been suggested (holding ctrl, holding shift, holidng ctrl+A, etc.) It seems that this solution is outdated, as most were posted in 2012 and 2015-16. A few of the comments also mentioned that things have changed for 2018, I don't know why. I'm attaching a screenshot of the spotify desktop app I am using on my Pixelbook.
p.s. I am trying to select from "My Songs" NOT a playlist