Wasn't the FED buying all the 2.5% mortgages?
That QE activity peaked circa Apr 2022[1].
The Fed subsequently announced monetary policy circa May 2022[2] to reduce the size of their balance sheet; with respect to agency mortgage-backed securities, that means predictably liquidating assets in the open market at a rate cap of $35 billion per month.
The Fed's weekly H.4.1[3] § 3 reports agency MBS assets are overwhelmingly residential. They were slowly ratcheting down commitments to buy MBS, and effectively reached 0 circa end of Oct 2022.
[1] https://fred.stlouisfed.org/graph/?g=ZcQw
[2] https://www.federalreserve.gov/newsevents/pressreleases/mone...