Bicameral Congressional Trade Authority Act of 2021 This bill requires congressional approval for a presidential import adjustment due to a national security threat from an import related to military equipment, energy resources, or critical infrastructure essential to national security. Specifically, the bill requires the President to submit a proposal to Congress, which Congress may approve by a joint resolution. Under current law, the President determines whether any adjustment of an import is necessary and must submit to Congress the reasons for any action taken or not taken. The Department of Defense (currently, the Department of Commerce) must investigate the effect of these imports on national security. The bill retroactively applies to any proposed action made four years before enactment of this bill. In general, any rate of duty modification occurring in the time period beginning four years before and ending the day before enactment of this bill must revert to the previous rate unless it receives congressional approval.