<p>The rapid growth of the Internet of Things (IoT) and its associated technologies has raised numerous challenges and concerns regarding security and privacy. Therefore, it is critically important to analyse the process of developing IoT applications for IoT-based systems (IoTSs) to understand how they are built and to identify the major privacy challenges involved. This paper aims to provide insights into the following topics: (i) the main issues related to IoT privacy during the development of IoT applications; (ii) the models and approaches currently being used in IoT application development; and (iii) how privacy aspects are incorporated into the stages of the IoTS development life cycle. A systematic mapping study (SMS) was conducted to identify and extract information from the most relevant papers on these topics. Accordingly, discussions, findings, results, and feedback from previous studies were analysed to create a comprehensive overview of the challenges and future directions. This SMS reveals important findings, including the need for further research and effort to systematically integrate privacy concerns into IoTS development models, highlighting the necessity of improved methodologies to address this crucial aspect of these systems.</p>