The End of Quantative Easing.

The 2008 Banking crisis, resulted in Central Banks globally bought assets of clearing banks, and crediting them with New money created by the Central Banks.

https://www.bbc.co.uk/news/business-63474176

Now the charts below show the US Federal Reserve, and you can see over a few months, it has shrunk the balance sheet from $8,945,898 Million ($8.945 Trillion) to $8,723,090 ($8.723 Trillion).

It is selling the US Treasury Bonds (T-Bonds = Treasuries) back to private investors, such as pension funds etc).