And some more precision: this is about the uppercase Eszett. The lowercase variant has existed for ages, and before 2017 was officially uppercased into SS or SZ.
It still is officially capitalized to SS under normal circumstances; capital ẞ is an allowed alternative: "Bei Schreibung mit Großbuchstaben schreibt man SS. Daneben ist auch die Verwendung des Großbuchstabens ẞ möglich." (Deutsche Rechtschreibung § 25 E 3)
SZ hasn't officially been an option at least since 1996.
SZ hasn't officially been an option at least since 1996.