The Atacama Cosmology Telescope: DR4 maps and cosmological parameters. Issue 12 (1st December 2020) - Aiola, Simone; Calabrese, Erminia; Maurin, Loïc; Naess, Sigurd; Schmitt, Benjamin L.; Abitbol, Maximilian H.; Addison, Graeme E.; Ade, Peter A. R.; Alonso, David; Amiri, Mandana; Amodeo, Stefania; Angile, Elio; et al.