If your metafield holds a numeric value, but the metafield value is indexed in the Algolia index as a string wrapped in quotation marks (for example, "1234"), you can double-check the metafield configuration in the Algolia Shopify app and verify whether the Conversion type is set to “Number.”
You can select “Number” as the Conversion type and initiate a full reindex. The metafield values should then be converted to numbers.