When the screen is off, draw || with two fingers on the screen at the same time to pause or play tracks, and draw < or > to switch tracks.
Setting method:
realme UI 5.0 & 4.0 & 3.0: Settings > System / Additional settings > Gestures & motions > Screen-off gestures > Music control
realme UI 2.0 & 1.0: Settings > Convenience tools > Gestures & motions > Screen-off gestures > Music control
realme UI R & Go & T & S & U Edition: not support
Related Articles:
How to set full screen gestures?
How to Switch to previous app under full screen gestures?