bencroker

{% set variantParam = 'variant' %}

{# set product #}
{% set product = craft.products.id(productId).one() %}

{# set variant #}
{% set variant = product.defaultVariant %}

{# overvrite default variant with url param #}
{% if product.variants|filter(v => v.id == craft.app.request.getParam(variantParam)) is not empty %}