The GDP-relative amount of US debt held by foreign investors has actually gone down on since 2014: https://fred.stlouisfed.org/series/HBFIGDQ188S

Am also casually looking at FRED. RE 2014 decline - do you know why this was? I speculate something to do with the initial invasion of Ukraine / China cycling out of treasuries possibly to buy Russian war bonds or oil. I am purely speculating.