Lawyers told the BBC that many families were persuaded to sign forms preventing them from taking legal action.
BBC Panorama has discovered that other relatives signed similar agreements after two other crashes, stopping them from suing Boeing in the US courts.
Boeing has declined to comment on the agreements.
All 189 passengers and crew died when the Boeing 737 Max crashed into the sea just 13 minutes after taking off from the Indonesian capital, Jakarta, on 29 October 2018.
Within weeks, relatives were offered compensation by insurance lawyers.