From this report https://www.usatoday.com/story/money/markets/2016/05/17/saud... it sounds like Saudi Arabia holds under $120 billion of US Treasuries with the total outstanding US debt being $21.702 trillion https://www.treasurydirect.gov/govt/reports/pd/mspd/2018/opd...

At 0.55% (the figure has possibly have gone down due to the drop in oil prices between 2016 and 2018) they're a significant holder, but hardly a market maker.