BACKGROUND With the digitalization of society and increasing loneliness due to population aging, the potential for digital loneliness interventions is growing. This article describes the mixed methods process evaluation of a digitally conducted randomized controlled trial, evaluating a mobile gaming application newly designed to improve the social connectedness of community-dwelling older adults. OBJECTIVE This paper aims to evaluate a social gaming application in community-dwelling older adults through a mixed-methods process evaluation of a digitally conducted randomized controlled trial (RCT). METHODS The RCT compared two gaming conditions with a control group. We included adults aged 65 years and over. The process evaluation involved a focus group and semi-structured interviews with the RCT participants and welfare organizations to explore barriers and facilitators for app usage and gameplay and analyzed questionnaire adherence, game engagement, network measures, and retention. RESULTS Of the 372 people who signed up for the RCT, 76 adults installed the app and signed informed consent, of whom 33 were 65+. The baseline completion rate of questionnaires was 36%, rapidly declining during follow-up. Participants experienced the app differently, varying from engaging to too simple or too complex. Participants suggested challenging and competitive games with increasing difficulty levels. Repeated instruction and in-person and personal contact were deemed essential to reach and engage the intended population. CONCLUSIONS Conducting a digital trial of a social gaming intervention for older adults is a great challenge. Evaluation of future digital gaming interventions should start with small-scale studies with personal contact and fewer questionnaires. CLINICALTRIAL ClinicalTrials.gov NCT04733898