Iranian Arms Transfer Prevention Act of 2021 This bill requires the President to impose certain property- and visa-blocking sanctions on persons determined to be involved in arms transfers to or from Iran. Specifically, the State Department must submit a biannual report listing each person that it determines is knowingly engaged in any activity contributing to (1) the supply, sale, or transfer to or from Iran of arms or related material; or (2) the proliferation of arms or related material by Iran or by paramilitary organizations supported by Iran. The President must impose sanctions on each foreign person listed in the most recent State Department report and on each foreign person the President determines engages in specified activities (e.g., providing Iran with technical training, financial resources or services, advice, or assistance related to the supply, sale, transfer, manufacture, or use of arms and related material).