Locking your account in your profile settings will make a universal change to your account.    You may choose to change each post privacy by using the globe icon in each gab post composer box.

Gab Profile Settings
https://gab.com/settings/profile

Each post composer box has a globe icon to choose the individual post privacy options:  Public, Unlisted or Followers only.
Note:  Profile pins can only be for posts (statuses) with public/unlisted visibility.   Only your own content can be pinned to your profile page.

* Federated timelines would be applicable for a decentralized instance.  Currently, Gab's servers are centralized.