The 21th Meeting on Off-Shell Science (, formally, Meeting on Dressed Photon and Off-Shell Science Theories) was held on December 15, 2021 (On line meeting). Eleven experts joined the meeting. Interesting topics on the nano-structure formation by dressed photon (DP), spontaneous symmetry breaking caused by DP, and numerical simulations of DP generation efficiency, were presented. Intensive discussions on these topics were made.