Filter runs based on tags, you need to modify the products first to make your filter work.
Step 1: From the Shopify Admin page > Products > pick a product.
Step 2: Scroll down and find the Tags section, add necessary ones for each product (size: S, M, L,... or color: white, red, etc.)
- For example: If I add Red and M tag for this item, it will show up as a result when the filter runs.
Step 3: Go to sidebar settings, write down all needed tags for filter selection and separate them by commas.
Step 4: Filter check.