Number format for wp_count_posts()

Question

You can use the PHP function number_format().

function wpb_total_posts() { 
    $total = wp_count_posts()->publish;
    echo number_format( 
        $total, // your number
        0,      // number of decimal points
        '.',    // decimal point separator
        ','     // thousands separator
    );
}

Or, because you are using the default values anyway, you can shorten the function to:

function wpb_total_posts() { 
    echo number_format( wp_count_posts()->publish );
}