Variant products in products grid

Dear customer support,
We are using the woodmart elementor product grid widget. We would like to choose some specific products to show in the grid. Therefore, we choose to set the specific list of products. However, we experiencing following issues:

1) If we would like to select a variant product to show in the grid, this doesn’t work – the product is not shown.
2) A more general question, why can we not choose the products based on the SKU but only based on the title?

Thanks