United States Commitment to Peacekeeping Act of 2021 This bill repeals a limit on U.S. funding for, details U.S. policy objectives for, and revises reporting requirements related to United Nations (U.N.) peacekeeping operations. Under current law, the United States may contribute no more than 25% of the assessed costs for a U.N. peacekeeping operation; the bill eliminates that funding restriction. The Department of State must instruct the U.S. Permanent Representative to the United Nations to advance the U.S. policy objectives outlined in the bill for standardizing performance assessments of, diversifying the funding base for, and other aspects of U.N. peacekeeping operations. The bill modifies annual reports about U.S. participation in U.N. activities by eliminating a requirement to report on costs of U.N. peacekeeping operations in the prior fiscal year and by adding a requirement to report on U.S. efforts to implement reforms of U.N. peacekeeping. Additionally, the State Department must report on (1) strengthening the role of conflict prevention in U.N. missions, and (2) transitioning U.N. peacekeeping operations to host-country security forces.