EN Express, no tablespace selection under storage
This happens when you log in to the root container of a CDB, because tablespaces are local to PDBs.

Configure EM Express at PDB level, for example:

connect / as sysdba
alter session set container=pdb1;
exec dbms_xdb_config.sethttpsport(5501);


Then log in to EM Express using port 5501.

PDB Tablespace is Not Showing in CDB 12c EM Express page (Doc ID 2278612.1)