Trump never conceded, he only cooperated
Presidency of Donald Trump
Trump refused to concede, and the administration did not begin cooperating with president-elect Biden's transition team until November 23.[854][855] In late December 2020, Biden and his transition team criticized Trump administration political appointees for hampering the transition and failing to cooperate with the Biden transition team on national security areas, such as the Defense and State departments, as well as on the economic response to the COVID-19 pandemic, saying that many of the agencies that are critical to their security have incurred enormous damage and have been hollowed out – in personnel, capacity and in morale.
https://en.wikipedia.org/wiki/Presidency_of_Donald_Trump