If you'd like to index metafields of type Text > Single line text > List of values (Shopify metafield content type), please make sure to select the Conversion Type as JSON Encoded. For example:
The values are correctly split into separate entries within an array, like ["Value1", "Value2", "Value3"].
You can also use the Single line text > One value content type:
Single line text > One value
Then, you would need to set the type conversion on the Algolia App for this metafield to String Array:
Algolia Search and Discovery > Indexing > Metafields indexing
Finally the values for this metafield on your products should be separated by a comma (,)
If you have set this metafield as a facet, this should be the output: