You may surprisingly see a credential dialog from XDB like the feature image when you tried to login Oracle Enterprise Manager Database Express (EM Express).
Rationale
This is because you have enabled the global port of EM Express for all containers. That is to say, all containers share one EM Express port.
Actually, the third field in the login page asks for a container name. What you should enter is not the database name, it's container name.
Let's see what container that we have.
SQL> column con_id format 99;
SQL> column name format a30;
SQL> select con_id, name from v$containers;
CON_ID NAME
------ ------------------------------
1 CDB$ROOT
2 PDB$SEED
3 ORCLPDB
Solution
OK, so we should NOT use ORCLCDB, instead we should use CDB$ROOT or any other container name.

Oracle Enterprise Manager Database Express 19c - NO Dialog
Then login.

Oracle Enterprise Manager Database Express 19c - CDB$ROOT
The new UI of EM Express may be unfamiliar to you. It's because EM Express adopts Java JET technology for its UI since 19c, if you'd like to old flash-based UI, you can switch EM Express 19c Back to Flash-Based.