Sorry to answer a question with a question, but why would you use an RMAN
duplicate if you were working with Multitenant?
We use lone-PDB for everything we can, or 3 PDBs on 19c. :) On those where
we have PDBs I never run an RMAN duplicate. I try to act like the CDB
doesn't exist. :) All clones are done using PDB clones. I see for the
banner you are on 12.2, so you can do hot clones, which are awesome. I've
just never felt the need to clone the CDB since I switched. It also means
renames are easy. :)