According to the United States Flag Code, specifically 4 U.S. Code § 6 and § 7, the flag is to be displayed at full staff on certain designated days, including Inauguration Day, unless there is a specific proclamation by the President or another authority to lower it to half-staff due to a national tragedy or mourning.
So again it would have to be Biden to proclaim it.
According to the United States Flag Code, specifically 4 U.S. Code § 6 and § 7, the flag is to be displayed at full staff on certain designated days, including Inauguration Day, unless there is a specific proclamation by the President or another authority to lower it to half-staff due to a national tragedy or mourning.
So again it would have to be Biden to proclaim it.