From 2019 to 2023, three universities – the National Institute of Oriental Languages and Civilisations, the University of Geneva, and the Beijing Language and Culture University – collaborated to produce a Massive Open Online Course (MOOC) entitled Initiation to the Dongba Script. The objective was to preserve and revitalise the Dongba script, an endangered writing system used by the Naxi people in southwestern China. The course aimed to engage learners around the world in learning the script and subsequently contributing to the preservation of this unique cultural heritage. Hosted by the French MOOC platform FUN, the MOOC ran for the first time from April to June 2023. Using a qualitatively led mixed research method integrating pre- and post-course questionnaire data, forum discussions, informal feedback, and fieldwork conducted in Lijiang in August 2023, this paper explores how participants experienced the MOOC as a learning and cultural engagement opportunity and which factors facilitated or constrained broader community participation, particularly from the Naxi community itself. The findings show that the MOOC successfully reached a highly educated, multilingual, international audience with strong intrinsic motivation. It achieved a completion rate more than double the global MOOC average, generating sustained post-course engagement across academic, creative and professional domains. The analysis reveals that, for many participants, the course functioned as a cultural threshold experience, repositioning the script from that of an unknown object to a personally meaningful one. Some learners went on to pursue academic research, creative applications, or further study of the Naxi language, suggesting the potential for longer-term engagement. These findings reveal a tension in MOOC-based heritage education: Open platforms can reach global audiences, yet local cultural transmission depends on sustained engagement with the living communities the heritage belongs to. They also offer valuable insights and lessons for digital heritage education initiatives in other endangered script contexts.