Hi,

There is a free module available in the Odoo store for the same, unfortunately, its version 11 is not available. You can get the V10 of the module from this link: Hide Inbox Chatter

You can try installing the v10 module in v11 and see whether it works fine, if not with a slight adjustment most probably it will work in v11.

Thanks

Create any new group after that add Discuss menu to this new group.

We have to hide the internal chat option. Because we are not allowing internal employees chat, I have to hide that completely.