Brown dwarfs serve as ideal laboratories for studying the atmospheres of giant exoplanets on wide orbits as the governing physical and chemical processes in them are nearly identical^(1,2). Understanding the formation of gas giant planets is challenging, often involving the endeav our to link atmospheric abundance ratios, such as the carbon-to-oxygen (C/O) ratio, to for mation scenarios³. However, the complexity of planet formation requires additional tracers, as the unambiguous …