Dreaming of being in a supermarket can symbolize a search for abundance or options in your life. It may reflect a desire to gather resources or make choices that contribute to your well-being. The act of singing and dancing to "Supermassive Black Hole" suggests a sense of freedom and joy, indicating that you might be embracing your individuality and expressing yourself without concern for how others perceive you.

The fact that some people smiled and enjoyed your performance may signify that you have a supportive environment or that you are more accepted than you realize. This could reflect a yearning for connection and the affirmation of your unique qualities.

Walking home after your shopping could symbolize a return to normalcy, integrating the happiness and confidence you experienced in the supermarket into your daily life. Overall, this dream seems to highlight themes of self-expression, joy, and the exploration of personal identity amidst societal expectations.