Shortcode to embed Edit Account form not working

You absolutely did not understand how the code from my previous answer works, yeah? The PHP ternary operator $result = $a ? $b : $c works the same way as the following construction:

if ( $a ) {
    $result = $b;
} else {
    $result = $c;
}

So the whole idea was to check if the get_user_meta(get_current_user_id(), 'last_name', true) function returns an empty value. When you change it to

($username = get_user_meta(get_current_user_id(), 'last_name', true)  . '</a>') ? ...

you break the whole logic, because that

get_user_meta(get_current_user_id(), 'last_name', true)  . '</a>'

string would never have an empty value (that should be quite obvious, even if the get_user_meta() function returns an empty value, the whole string would be equal to '</a>'). Use this statement:

return '&nbsp;<a href="' . admin_url('profile.php') . '">' . ( ( $username = get_user_meta( get_current_user_id(), 'last_name', true ) ) ? $username : ">Noe Name [edit profile]" ) . '</a>';

Update

If you want to work with several user meta fields, I recommend to use get_userdata() function:

function colaborador_nome($atts)
{
    if (is_user_logged_in() && !is_feed()) {
        $userdata = get_userdata( get_current_user_id() );
        $username = trim( implode( ' ', array( $userdata->first_name, $userdata->last_name ) ) );
        return '&nbsp;<a href="' . admin_url('profile.php') . '">' . ( $username ? $username : ">Noe Name [edit profile]" ) . '</a>';
    }
}

I still don’t understand why the shorthand form of ternary operator doesn’t work for you, using it would help to simplify the return statement to

return '&nbsp;<a href="' . admin_url('profile.php') . '">' . ( $username ?: ">Noe Name [edit profile]" ) . '</a>';