Man pages matching name mpi_type_get_true_extent in section 3:

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