Mpi error when running ff-mpirun on Ubuntu 20.04.2 LTS

error while loading shared libraries: libmpi_cxx.so.20: cannot open shared object file: No such file or directory

I am sure libopenmpi-dev has been install already.

Please can anyone suggest what’s wrong?

I followed the guideline for Ubuntu installation, and installed
FreeFEM_4.9_Ubuntu_withPETSc_amd64.deb

BTW, serial FreeFem++ command works well.