I'm not a fan of Barr either, but this may not be what it looks like. Note I said "may."

He appears to be saying that Durham's investigation won't get the Bidens vis-a-vis Burisma or China because they are not directly involved with the coup plot. Durham is investigating what happened within the intelligence apparatus and the White House to frame Trump and try to remove him. While Biden was involved with that, his son was not and it is unrelated to Ukraine or China.

The Biden family corruption is an entirely different problem unrelated to the coup. If anything, Biden should be investigated by a Special Counsel that should be investigating corruption within the State Department regarding the entire impeachment/whistleblower bullshit.