Cosmic molecular gas-mass density in group environments derived using the group identified by MUSE and detected by ALMA in CO (2-1) at z = 1.284 (blue data point and error bar). For reference, literature estimates are also included. The CO-derived estimates reported by Decarli et al. (2020) from z = 0.271 to 4.475 appear as filled grey boxes, and those at 1 ≲ z ≲ 3 reported by Messias et al. (2024) appear as empty boxes. The sub-millimeter continuum derived trend from Scoville et al. (2017) is displayed as a continuous filled grey region. The cosmic mass density is plotted as the ratio to the critical cosmic density.