Is it possible to remove the Add topic ( click the top right pointer for chatter feed) inside the section as we need to prevent end users from creating the topic. Can this be customized? Any org level setting for this ?
There are four General User Permission settings that are related to topics:
Create Topics: Allows a user to create a new topic for comments and posts.
Assign Topics: Allows users to assign existing topics to comments and posts.
Edit Topics: Allows a user to edit existing topics.
Delete Topics: Allows users to delete existing topics. The user would also need access to the 'Modify All Data' permission.
Removing the 'Create Topic' setting for the relevant profiles in your org will ensure that they are not able to create new topics. And if you don't want users interacting with topics at all on chatter posts, I would make sure all the settings above are unchecked on the profile.