On the 8th and 9th June 2021, the 4th annual ScyLight workshop took place online. This year the annual event took place online due to the COVID-19 pandemic. Nonetheless, the event was attended by 284 attendees, totalling 382 registrations to the event, including national delegations, industrial representatives of ESA Member States, ESA staff members and academic researchers. It once more provided the opportunity to present outcomes of ongoing activities in industry, academia and agencies as well as the right occasion to provide an overview of on-going ESA activities under the ARTES 4.0 Strategic Programme Line Optical Communication - ScyLight.