EM Express for PDB
During database creation, DBCA enables Enterprise Manager Express (EM Express) for being created CDB, not for PDB globally by default. We can either:
Solutions
1. Enable Global Port
To share the port (i.e. 5500) for all PDB globally, we can do it like this.
[oracle@ora19c1 ~]$ sqlplus / as sysdba
...
SQL> exec dbms_xdb_config.setglobalportenabled(TRUE);
PL/SQL procedure successfully completed.
Then we go for EM Express.
https://ora19c1.example.com:5500/em
Carefully enter the PDB name in the field of "Container Name".

EM Express Global Port for all PDBs
2. Enable a Separate Port
We can also assign a dedicated port for each PDB.
A. Open the PDB
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 ORCLPDB1 MOUNTED
SQL> alter pluggable database ORCLPDB1 open;
Pluggable database altered.
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 ORCLPDB1 READ WRITE NO
B. Set Current Container
SQL> alter session set container=ORCLPDB1;
Session altered.
SQL> show con_name
CON_NAME
------------------------------
ORCLPDB1
C. Check Current Port of EM Express
SQL> select dbms_xdb_config.gethttpsport() from dual;
DBMS_XDB_CONFIG.GETHTTPSPORT()
------------------------------
0
Obviously, there's none, we have to set one for the PDB.
D. Set EM Express Port
SQL> exec dbms_xdb_config.sethttpsport(5501);
PL/SQL procedure successfully completed.
SQL> select dbms_xdb_config.gethttpsport() from dual;
DBMS_XDB_CONFIG.GETHTTPSPORT()
------------------------------
5501
1 row selected.
Now go to the following URL for signing on EM express of the PDB. In this case, I go for:
https://ora19c1.example.com:5501/em
The new interface of EM express 19c may not have as many features as used to be, but you can revert it back to flash-based EM express.