Approval Notification should not disappear from the bell icon

Summary:

Notifications in the bell list are purged thirty days after their creation date regardless of their state (read or not) or the corresponding tasks state (completed or not). But our client requirement is that the notification should not disappear from the bell icon. Is there any way we can achieve this?

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):