Question:

 After updating my device to Android S OS (One UI 4), why isn't the music control widget showing up on my Lock screen for apps like YouTube, YouTube Music, or Vide?

Answer:

With the new concept introduced in Android S OS, the music control widget on the Lock screen appears only when both the media app's notification and the Lock screen's music widget settings are enabled. This allows you to choose whether or not to display the music widget based on your personal preferences. To fix the issue, follow these steps:

Enable notifications for your media app:

Go to Settings > Notifications > Apps.

Find the media app you use (e.g., YouTube, YouTube Music) and turn on its notification option.

Enable the music widget setting on your Lock screen:

Go to Settings > Lock screen > Widgets.

Turn on the Music widget to show the music controller on the Lock screen.

If you prefer not to see the music controller, simply turn off the Music widget.