Although this article adds some new specifics:

Durham "has requested Mr. Brennan’s emails, call logs and other documents from the C.I.A."

The underlying info is not really that new. https://www.nytimes.com/2019/12/19/us/politics/durham-john-brennan-cia.html

We knew of this official shift in Durham's focus towards Brennan & Clapper in late October.

The August & late September trips to Italy to meet with Italian law enforcement and Intelligence officials appears to have been the impetus. https://www.theepochtimes.com/focus-of-durham-probe-shifts-to-senior-obama-officials_3125706.html

Durham’s last known visit to Italy was made in late Sept. 2019, indicating that his advisement to Horowitz:

"last month we advised the Inspector General that we do not agree with some of the report’s conclusions"

was made in the weeks immediately following Durham’s Italy trip.