BBH populations for different metallicities (Z = 0.02 in the left column, Z = 0.002 in the central column, and Z = 0.0002 in the right column) and cluster environments, namely YCs (upper row), GCs (central row), and NCs (bottom row). The bins are normalized over the number of BBHs, with brighter (darker) colors corresponding to more (less) BBHs. The GW231123 primary and secondary masses are indicated with a red cross. The fraction of BBHs falling within the event mass ranges is indicated for each metallicity–environment combination in the plots.