@Sbectol tricky question. Unless you manage your followers and set toots to followers-only, then technically you have chosen to publicly broadcast your content. So it's in the ether at that point, and you cannot control what remote servers do and don't do.
See https://github.com/joyeusenoelle/GuideToMastodon#so-if-i-lock-my-account-only-approved-people-can-see-my-posts for better context