One of the disadvantages of the YouTube Music app for non-subscribed users is that the music cuts out as soon as you switch to another app.
Music available in the background on YouTube Music in Canada, for starters?
Until then reserved for those who pay a subscription, the background music playback function is now available to everyone from November 3 ... but only in Canada to begin with. In its announcement post, however, Google specifies that new information and plans for expansions will be revealed.
It's a safe bet that the functionality could be extended to other parts of the world in the coming times.