If you try to create 4 or more PDB in a container then you might get below error.

SQL> create pluggable database ADMIN USER pdb_admin identified by *** DEFAULT TABLESPACE USERS;
Enter value for p: TEST
old 1: create pluggable database &p ADMIN USER pdb_admin identified by *** DEFAULT TABLESPACE USERS
new 1: create pluggable database TEST ADMIN USER pdb_admin identified by *** DEFAULT TABLESPACE USERS
create pluggable database TEST ADMIN USER pdb_admin identified by *** DEFAULT TABLESPACE USERS
*
ERROR at line 1:
ORA-65010: maximum number of pluggable databases created

error details:

$ oerr ora 65010
65010, 00000, "maximum number of pluggable databases created"
// *Cause:  User attempted to create more than supported
//          number of pluggable databases.
// *Action: Avoid creating too many pluggable databases.
//

If you check the “max_pdbs” parameter value it is set very high (4098).

SQL> sho parameter max_pdbs

NAME                     TYPE              VALUE
------------------------ ----------------- ---------------
max_pdbs                 integer           4098

If you try to change or reduce this parameter value, you would still get an error.

SQL> alter system set max_pdbs=25;
alter system set max_pdbs=25
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-65334: invalid number of PDBs specified

From Oracle 19c on you can have 3 user-created pluggable databases of any type without a Multitenant license. If you have the need for 4 or more PDBs within one container database, you will need a Multitenant license.