The installation, unveiled during World Health Assembly week, features 50 illuminated lightboxes displaying the lock-screen photographs of children who lost their lives following online violence or digital harm.
Markle appeared without her husband, Prince Harry, 41, who has also publicly campaigned against the dangers posed by social media to young people.
The event included WHO director-general Tedros Adhanom Ghebreyesus, ministers, health officials, and families personally affected by online abuse.
One source familiar with the reaction to the event said the sparse turnout quickly became a talking point.
The insider added, “There was surprise among some observers because Meghan remains one of the most internationally recognized women in the world, yet the atmosphere around the event felt surprisingly subdued. A lot of people expected a much larger public response given the amount of media attention that usually follows her.”