Hello,

By default, the Product Grid element can show 2 products on mobile and this is cannot be changed.

You can create two rows with the Product Grid carousel element and configure one row for 3 items per row, and show it only on desktop, and another only for mobile and with one item in the row http://prntscr.com/qpl8tv

You can find the instruction on how to configure the Product Grid element here: https://xtemos.com/docs/woodmart/faq-guides/product-grid-carousel-element/

Best Regards