You can either put the classes on the “row” or the “column”?
Won’t be visible on the cards (border) if you use it on the row.
https://getbootstrap.com/docs/4.6/utilities/flex/#align-items
<div class="container">
<div class="row">
<div class="col-lg-4 d-flex align-items-stretch">
<!--CARD HERE-->
</div>
<div class="col-lg-4 d-flex align-items-stretch">
<!--CARD HERE-->
</div>
<div class="col-lg-4 d-flex align-items-stretch">
<!--CARD HERE-->
</div>
</div>
</div>
UPDATE BS5 FULL HTML EXAMPLE