Verify if the client is connecting to the Oracle database using native network encryption
You're confused with my comments,with accepted on server side and required client side sqlplus connection is encrypted and Sql Developer with thin client  is unencrypted but the same Sql Developer with thick client connection is encrypted.(Toad is out of scope I never used at all).In other words accepted on server side is working as expected.
Let me demonstrate for you
 sqlnet.ora on server 

    $ cat $TNS_ADMIN/sqlnet.ora
    # sqlnet.ora Network Configuration File: /u01/app/oracle/product/19/network/admin/sqlnet.ora
    # Generated by Oracle configuration tools.
    
    NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME)
    
    SQLNET.ENCRYPTION_SERVER = accepted
    
    SQLNET.ENCRYPTION_TYPES_SERVER= (AES256)
    
    SQLNET.CRYPTO_CHECKSUM_SERVER = required
    
    [CDB2] oracle@hol:~
    
   Client side Window 10 Pro

sqlnet.ora

# sqlnet.ora Network Configuration File: C:\app\oracle\product\19.3.0\db_1\network\admin\sqlnet.ora
# Generated by Oracle configuration tools.

# This file is actually generated by netca. But if customers choose to 
# install &quot;Software Only&quot;, this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

#SQLNET.ENCRYPTION_CLIENT=REQUIRED   -- commented out
#SQLNET.ENCRYPTION_TYPES_CLIENT=(AES256) -- commented out



    SQL&gt; @network_encryption

NETWORK_SERVICE_BANNER
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TCP/IP NT Protocol Adapter for Linux: Version 19.0.0.0.0 - Production
SHA1 Crypto-checksumming service adapter for Linux: Version 19.0.0.0.0 - Production
Crypto-checksumming service for Linux: Version 19.0.0.0.0 - Production
Encryption service for Linux: Version 19.0.0.0.0 - Production

Now I'll uncomment last two lines in sqlnet.ora client side
# sqlnet.ora Network Configuration File: C:\app\oracle\product\19.3.0\db_1\network\admin\sqlnet.ora
# Generated by Oracle configuration tools.

# This file is actually generated by netca. But if customers choose to 
# install &quot;Software Only&quot;, this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

SQLNET.ENCRYPTION_CLIENT=REQUIRED

SQLNET.ENCRYPTION_TYPES_CLIENT=(AES256)




ADR_BASE = C:\app\oracle\product\19.3.0\db_1\log


SQL&gt; @network_encryption

NETWORK_SERVICE_BANNER
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TCP/IP NT Protocol Adapter for Linux: Version 19.0.0.0.0 - Production
AES256 Encryption service adapter for Linux: Version 19.0.0.0.0 - Production
SHA1 Crypto-checksumming service adapter for Linux: Version 19.0.0.0.0 - Production
Crypto-checksumming service for Linux: Version 19.0.0.0.0 - Production
Encryption service for Linux: Version 19.0.0.0.0 - Production.

Now let's test with Sql Developer thin client

It's evident from above image it uses jdbc thin driver.Let's check the sql out put in Sql Developer and as expected there is no AES256  encryption

Now I will switch to thick client,check both images


Hope this clears up