Google seems to have recently been reminded of the existence of homescreen widgets on Android. After adding a widget for Tasks, another relatively new Google app is getting the same treatment: YouTube Music.
Perhaps it was the hullaballoo with Spotify's widget that reminded the YouTube Music team its app still lacks one, or maybe this was already on the roadmap but had to be thoroughly tested. Either way, you can now tap and hold on your homescreen to add a widget, scroll down, and pick the YouTube Music one. It can only be resized to 4x1 or 5x1 (i.e. you can't make it taller or square), and contains all the buttons you need quick access to: playback controls, thumbs up, and thumbs down. (They're also the same ones you get in the notification.)
To get the widget, you need YouTube Music v3.39, which is available on the Play Store or downloadable from APK Mirror.