How to hide post content/meta from everyone except the post author and admin

by

You can try below code –

<?php
    global $current_user;


     if ((is_user_logged_in() && $current_user->ID == $post->post_author) || current_user_can( 'manage_options' ))  {
        echo 'my post';
    }
?>

Check below link also-

https://codex.wordpress.org/Function_Reference/current_user_can