Digitalization of Smart City—Sine Qua Non or an Option for Those Interested?

A common feature of numerous definitions of “smart city” is the skilfull use of digitalization tools aimed at achieving the goals of urban policy based on the principles of sustainable development. Digitalization is, therefore, the foundation of a smart city, however, there are no uniform standards for digital solutions that city authorities could implement. This article aims to analyze digitalization solutions understood as processes implemented in the cities ranked in the first five positions of the latest Smart City Index report for 2021—Singapore, Zurich, Oslo, Taipei City, and Lausanne. The authors show whether—and to what extent—digitalization of smart cities is a defining condition for their status and to what extent it is optional. The study showed that various digitalization solutions and paths were implemented, however, their scope and goals differ depending on the specificity of each city and the municipal strategy implemented.