Meaning
A few musical notes floating together, as if a tune is drifting through the air. It signals music in general: singing, humming, a song stuck in your head or a good playlist.
People add it when sharing a track, quoting a line they love, or describing a cheerful mood: “Cleaning the whole house with my favorite playlist on 🎶” It can also mark a message as sung or playful, like a tiny jingle. Sometimes it is used sarcastically to pretend not to hear something, a sort of humming to change the subject.