The 2021 defense appropriations bill maintained a congressional ban on any funds “to construct or modify facilities in the United States to house detainees” transferred from the Guantanamo Bay naval base in Cuba. Congress has consistently blocked such moves after President Obama’s early attempts to follow through on his campaign vow to close the prison set up there after 9/11.
President Biden has expressed support for closing the prison both prior to and during his presidential campaign, in a 2019 debate calling the continuing detention of 40 people there “an advertisement for creating terror.”
Biden has options to restart the closure process that don't need congressional approval. He can resume the transfer of detainees to other countries, rescind President Trump's 2018 executive order keeping Guantanamo open and issue new executive orders reinstating closure as official U.S. policy.