Full context from the article:

Holdings of U.S. Treasuries slipped to $9.299 trillion in June from $9.371 trillion in the previous month. But compared with a year earlier, Treasuries owned by foreigners were up 2.3%.

Also relevant context are the various exchange rates to foreign countries... Not going to list all of them but here's to a multi-currency index: https://www.marketwatch.com/investing/index/dxy

As well remember this is a nominal number.

Edit to add: the fact that it's going down is not great, but the headline references only monthly which is noisy. Here's also a trend over time from FRED (quarterly): https://fred.stlouisfed.org/series/FDHBFIN

TLDR: this might just be a blip, not really any bigger news than the stock market being slightly down any given month. As much as I dislike the current administration don't add this to your doom scrolling just yet.