Abstract Digital health interventions (DHIs) can facilitate positive health outcomes. User engagement (UE) plays an important role in DHI efficacy. Yet, DHIs vary in functionality, design and intended outcomes, underscoring the importance of incremental, user-centred design to understand engagement in specific settings. This study explores the relationship between user engagement and DHI implementation in three design iterations, or rounds, of a unique, multi-week asynchronous intervention that leverages online discussion and problem-solving therapy (PST). The intervention seeks to engage older adults to improve problem solving skills relating to the intervention focus, health aging (two rounds) and Lewy Body Dementias (LBD) caregiving (one round). The PST component drew upon personas, a common user-centered design method, in a novel way. Exit interviews were conducted at the end of each round to understand participants' experiences. Using thematic analysis, we identified factors that contributed to social engagement (‘engaging with others’) and learning engagement (‘engaging with content’) with the DHI. The findings demonstrate how iterative changes in the design and delivery of a DHI can contribute to user engagement, increasing the likelihood of knowledge acquisition and developing problem-solving skills as part of health self-management.