YouTube Music is slated to replace Google Play Music later this year. There are still some discrepancies and missing features, and Google is hard at work bringing over as much functionality to its new music streaming service as it deems feasible and necessary. As such, YouTube Music now tests displaying albums and playlists that you've saved to your library in the Last Played overview.
The change is only available for a few people who got in on a server-side a/b test. To check if it's live for you, just add any album or a playlist to your YouTube Music library and head to the library tab — in your Last Played overview up top, you should see the newly added tracks (though you might need to pull-to-refresh first). You can see this in the screenshots below, coming courtesy of a Redditor. That's the behavior we know from Play Music — albums and playlists you add to your library show up in the app's Recents section among music you've listened to. The section has also been renamed from "Last played" to "Recent activity" in Portuguese, so we'll likely see a similar fitting change in English.
Left: Add a playlist or album to your library... Middle: ...and it will show up in your history.
It looks like the new history isn't widely available yet as we can't reproduce this on our own devices, so if this isn't live for you, there isn't much you can do. It's still a good idea to stay up to date if you're hoping to get in on tests like these, so be sure you're on the latest version of the app available on the Play Store or APK Mirror.
Updated to reflect the name change from "Last played" to "Recent activity," as pointed out by P3dRo in the comments (Thanks!).
- José & Moshe