Why do I get ORA-12541: TNS:no listener when trying to select from a CDB to its PDB using a dblink.

(Note: I originally asked this question in a totally incorrect spot, so I'm just going to copy and paste it the way I wrote it without re-editing it to combine my comments)

We're on oracle 19.7 and starting to convert our stand alone databases to multitenant.

For reference here is the CDB and its PDBs:

SQL> @whereami

INSTANCE CONTAINER  USERNAME

---------- --------------- ------------------------------

CDB19CT1 CDB$ROOT  SYS

SQL> show pdbs

 CON_ID CON_NAME      OPEN MODE RESTRICTED

---------- ------------------------------ ---------- ----------

   2 PDB$SEED      READ ONLY NO

   3 COTDEV       READ WRITE NO

   4 PDB19CT1      READ WRITE NO

When I'm connected to the CDB in sqlplus, I can not connect to its PDB using an implicit database link. I get ORA-12541: TNS:no listener.