The COVID-19 pandemic and the implementation of large-scale social restrictions have caused economic and social disruptions globally, including in Indonesia. These difficult situations have shifted the financial attitudes, especially among the working-age group in Indonesia, to be more focused on saving and investing. One of the popular options among new investors is mutual fund investment because it requires a lower cost than other options, offers diversified holdings, and supports a variety of risk profiles. New investors primarily use an investment app, such as a mutual fund investment application, to manage their investment portfolios safely and seamlessly. In line with the rapid growth of mutual fund investors, the number of mutual fund investment apps in Indonesia has increased to more than 80 providers in 2022, resulting in fiercer competition between service providers. Therefore, retaining and increasing the apps’ investment usage is crucial to providers’ business success. This study investigates factors affecting the investor’s continuance intention to use mutual fund investment apps by adapting the expectation-confirmation model (ECM) with other key constructs, i.e., perceived security, trust, and self-efficacy. The collected data from 384 participants were analyzed using Structural Equation Modelling. The results indicate that perceived usefulness, trust, and user satisfaction positively affect the continuance use of mutual fund investment apps. Based on findings, this study proposes practical strategies to retain the application usage, such as implementing security measures, personalized investment courses and advisories based on the user’s profile risks and preferences, and recommendations on achieving the user’s investment goals based on machine learning solutions. Digital solutions, such as financial and investment apps, may contribute to expanding access to banking, financial services, and financial inclusion in the Indonesian population.