Actually, there is a jQuery selector just for this, :checked
So something like this:
{"_id":"forum-holos","startUrl":["https://holos.ie/product/this-is-more-range-samples/"],"selectors":[{"id":"Title","type":"SelectorText","parentSelectors":["_root"],"selector":"div > h1","multiple":false,"regex":""},{"id":"dropdowns","type":"SelectorElementClick","parentSelectors":["_root"],"selector":"div.elementor-jet-single-add-to-cart","multiple":true,"delay":"2250","clickElementSelector":"td.value select > option[class^='attach']","clickType":"clickOnce","discardInitialElements":"discard-when-click-element-exists","clickElementUniquenessType":"uniqueText"},{"id":"Variation Title","type":"SelectorText","parentSelectors":["dropdowns"],"selector":"td.value select > option:checked","multiple":false,"regex":""},{"id":"Price","type":"SelectorText","parentSelectors":["dropdowns"],"selector":"span.price","multiple":false,"regex":""}]}
Ref: Selectors | jQuery API Documentation