Man pages matching name mpi_comm_dup_fn in section 3:

MPI_COMM_DUP_FN.3.en	debian 10 / lam4-dev
MPI_COMM_DUP_FN.3.en	debian 11 / lam4-dev
MPI_COMM_DUP_FN.3.en	debian 12 / lam4-dev