United Nations Transparency and Accountability Act of 2021 This bill requires various actions related to malign influence operations by other countries in the United Nations (UN), with such operations defined as coordinated actions by a UN member state to foster UN actions or attitudes that further that member state's interests in a manner inconsistent with the UN Charter. The President shall direct the U.S. Permanent Representative to the UN to vote for and promote policies to (1) oppose malign influence operations and UN employees involved in such operations, and (2) support Taiwan's membership or meaningful participation in UN entities. (Taiwan was expelled from the UN in 1971.) The Department of State shall designate a senior level official to assist in implementing such policies and fulfill other related responsibilities. The State Department shall also establish an Office of Multilateral Strategy and Personnel within the Bureau of International Organization Affairs to promote the candidacy of U.S. citizens for roles in international organizations, including the UN, and to coordinate support for non-U.S. candidates when appropriate. The State Department shall increase by at least 50% the number of U.S.-sponsored Junior Professional Officer positions in the UN. The President shall periodically review evidence and determine if any countries have engaged in malign influence operations that have threatened U.S. interests. The President must designate any such country as a malign global actor and provide an explanation to Congress for why the designation was made.