My Application is still accessible even after logging out of Okta

@Suchina.N
Did you clear Okta session when you logout?
Here is a way to delete the user’s all sessions and you can implement it when you call logout function.
Revoke and clear session and token

The sessions endpoints can be used to logout a user and also revoke all tokens associated with the user:
DELETE: /api/v1/users/ ${userId} /sessions?oauthTokens=true
https://developer.okta.com/docs/reference/api/users/#user-sessions
The api collections can also be found in the above link.
userId is the “sub” value in id token or the “uid” value in access token.

Here is more reference:
https://developer.okta.com/docs/guides/sign-users-out/android/sign-out-of-okta/

Let me know if the above info is helpful