[oracle@xhydra DB9ZX]$ oerr ora 00059
00059, 00000, "maximum number of DB_FILES exceeded"
// *Cause:  The value of the DB_FILES initialization parameter was exceeded.
// *Action: Increase the value of the DB_FILES parameter and warm start.

kIsH@Xhydra<>startup force;
ORACLE instance started.

Total System Global Area 1962932632 bytes
Fixed Size                  9136536 bytes
Variable Size            1325400064 bytes
Database Buffers          620756992 bytes
Redo Buffers                7639040 bytes
ORA-00059: maximum number of DB_FILES exceeded

kIsH@Xhydra<>select status from v$instance;

STATUS
------------
STARTED

Check the parameter db_files

kIsH@Xhydra<>show parameter db_files

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_files                             integer     25

kIsH@Xhydra<>show parameter db_create_file

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_create_file_dest                  string      /apps01/oradata

Increase the value for number of datafiles

kIsH@Xhydra<>alter system set db_files=200 scope=spfile;

System altered.

kIsH@Xhydra<>startup force;
ORACLE instance started.

Total System Global Area 1962932632 bytes
Fixed Size                  9136536 bytes
Variable Size            1325400064 bytes
Database Buffers          620756992 bytes
Redo Buffers                7639040 bytes
Database mounted.
Database opened.
kIsH@Xhydra<>select count(*) from v$datafile;

  COUNT(*)
----------
        26

kIsH@Xhydra<>exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
[oracle@xhydra DB9ZX]$ tree|awk '{print $3}'|grep '.dbf'|wc -l
22