Hi Daniel,
I am sorry for the late response. Thank you so much for your help!
Yes, I am sure it is the same version. I tried VScode and this error disappeared for few days, and today I tried again and it re-appeared.
Now it has
1) mpi.h{Ln140, Col 27]: unknown type name 'MPI_Comm'
2) exceptions.h[Ln 1743, Col 12]: unknown type name 'DEAL_II_HOST_DEVICE'
3) all the errors in mpi.h in deal.II/base/mpi.h, identifier :MPI_Comm", "MPI_Request', "MPI_Group" "MPI_Datatype" .... undefined.
I am not sure if these are related with deal.II or VScode.
Sincere thanks and Best regards,
H