In Oracle 19c database, how can I find out tablespace, schema, tables allowed to access, privileges assigned to a user grouping by that username?

Are you looking for something like this?

Replace USER with the desired username

Granted Roles:

SELECT * 
  FROM DBA_ROLE_PRIVS 
 WHERE GRANTEE = 'USER';

Privileges Granted Directly To User:

SELECT * 
  FROM DBA_TAB_PRIVS 
 WHERE GRANTEE = 'USER';
Privileges Granted to Role Granted to User:

SELECT * 
  FROM DBA_TAB_PRIVS  
 WHERE GRANTEE IN (SELECT granted_role 
                     FROM DBA_ROLE_PRIVS 
                    WHERE GRANTEE = 'USER');
Granted System Privileges:

SELECT * 
  FROM DBA_SYS_PRIVS 
 WHERE GRANTEE = 'USER';

If you want to lookup for the user you are currently connected as, you can replace DBA in the table name with USER and remove the WHERE clause.