If you are building a website for a client and there is no need for them to access the "post", for example, if they are not going to do any blogging, then use the code below to remove it from the sidebar.
The result will be that the "Posts" button is removed from the sidebar so client cant access it.
NOTE: deregistering the post type completely is NOT RECOMMENDED, so whilst you can "hide" the link to posts type, avoid deregistering.
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# Remove default post type from admin bar
# See: https://www.jucra.com/whmcs/knowledgebase/126/
####################
add_action( 'admin_menu', 'remove_default_post_type' );
function remove_default_post_type() {
remove_menu_page( 'edit.php' );
}