Bootstrap 4 right Column on top on mobile view

Answer 1

have you tried like this

<div class="row">
    <div class="col-md-8 col-sm-8 col-xs-8">
        A
    </div>
    <div class="col-md-4 col-sm-4 col-xs-4">
       B
    </div>
</div>

The Bootstrap grid system has four classes col-xs, col-sm, col-md, col-lg. That classes can be combined to create more dynamic and flexible layouts.

Answer 2

With Bootstrap 4 you can use the following classes.

order-first, order-last and order-0 - order-12

on your element.

Have a look here: Column ordering in Bootstrap 4