Hi,
I created new item using React for frontend and BigCommerce for backend. Which category should I choose?
or
Kind Regards,
Nine-Themes
or
I’ll speak now as a ThemeForest customer 
When I search themes, I usually search them by the technology used in the back-end (Shopify, BigCommerce, etc) not by the name of the JavaScript library used to build the front-end (they are so many nowadays 
).
So I’d say to post it in the BigCommerce category, but it’s just my personal opinion; maybe more experienced ThemeForest authors can help us here with their feedback…