Animal Crossing doesn’t offer much in terms of settings, but because the game has been designed with a young audience in mind by default, this isn’t really an issue.
The NIntendo Switch device does have privacy settings. By selecting ‘User Settings’, you can then scroll down to ‘Friend Functions’ and select ‘FriendSettings’. From here, you can choose from ‘All Friends’, ‘Best Friends’ or ‘No One’; the latter two being the safer options.