Using APEX 21.1 and ORDS 21.2 in a new Oracle Database XE 18c fresh install.
APEX 21.1 installed normally as usual. But after installed ORDS, got error '404 not found' when trying to access url http://<host>:<port>/ords.
Watching at /opt/oracle/ords/config/ords/conf, only present APEX_PU.XML file which contains user ORDS_PUBLIC_USER and password.
APEX.XML file was not present so not created with ORDS installation.
Fixed just copying APEX_PU.XML as APEX.XML and then changing user ORDS_PUBLIC_USER as APEX_PUBLIC_USER. Maintain encrypted password as you passed it in installation.
Starting again ORDS, or container, will not longer get error "404 not found" and apex starts login as usual.