Man pages matching name mpi_type_dup in section 3:

MPI_Type_dup.3.en	debian 10 / lam4-dev
MPI_Type_dup.3.en	debian 10 / mpich-doc
MPI_Type_dup.3.en	debian 11 / lam4-dev
MPI_Type_dup.3.en	debian 12 / lam4-dev
MPI_Type_dup.3.en	debian 12 / mpich-doc