Antony Blinken, Biden's nominee for Secretary of State, has worked closely with the President-elect through much of the past two decades, first as a Senate staffer and then in the Obama admnistration.
He has called Biden's support for the Iraq War in a Senate vote in 2002 a "vote for tough diplomacy," arguing that it increased the likelihood of successful diplomacy.
Blinken's direct role in key Obama-era decisions on Libya (to support intervention) and on Afghanistan (to increase troop commitments, over Biden's opposition) isn't clear. In a 2020 CBS interview, he criticized Trump administration withdrawals from Syria, while admitting the Obama team's own efforts "failed."
In 2018 Blinken joined other Obama-era officials criticizing U.S. support of the Saudi-led coalition in the "disastrous" war in Yemen, which actually began in Obama's tenure but expanded under Trump.