You can create filters based on metafield using the following steps:
Go to your Shopify Admin Store > App > Searchly.
Click on Filters and select Manage Filters.
Click on Add New Filter.
Type filter title in Title field, select Product Metafield in Created Filter Using field.
Enter Product Metafield based on which you would like to create a filter and click Save.
Run data sync by clicking Data Sync.
Please see this example for reference:
Filter created by Metafield.
( Note: Metafields are not comma separated in Metafield name field, you must create each filter for each metafield )