How do I make my X (Twitter) account private so only approved followers see my posts?

Go to Settings and privacy > Privacy and safety > Audience and tagging > toggle on 'Protect your posts' (same path on mobile). Once on: only approved followers see your posts, new follow requests need your approval, your posts stop showing in public search and can't be reposted, and replies you send to non-followers won't be visible to them. Existing followers stay unless you remove them. What it does NOT do: hide posts that were public in the past from people who already saw or saved them, and your bio and photo stay visible. It's the right move for a locked-down, follower-only account.