Axios (Shawna Chen) reports, as does an opinion piece in the Washington Post (Josh Rogin) (paywalled). From the Post:
[L]ast November, when [American citizen Saad Ibrahim Almadi] traveled to Riyadh to visit family, he was detained regarding 14 tweets posted on his account over the previous seven years. One of the cited tweets referenced Jamal Khashoggi, the Post contributing columnist who was murdered by Saudi agents in the Saudi Consulate in Istanbul in 2018. Other tweets criticized the Saudi government's policies and the corruption in the Saudi system.