You make it sounds like they aren't doing regular open market operations, but as I understand it... they still do?
https://www.newyorkfed.org/markets/domestic-market-operation...
The Fed still does purchases and sales, but not for the purpose of driving the overnight interest rates towards its target. The level of the overnight rate is not affected of any purchases or sales that the Fed does.
If the Fed makes or receives a loan at specific interest rates (even if only overnight), that's pretty much economicaly equivalent to buying or selling bonds.