Both the multi match query and simple match query are the search types for the frontend. The main difference between the two in Magento 2 Elasticsearch is that:
In case of multi match query, a customer can search the data by multiple fields such as name, SKU, description, short description or the attributes defined by the admin.
However, in case of simple match query, the customer can search products by limited fields such as name or SKU.
Please do contact us for any further queries or requirements. You can also check our Magento 2 Extensions for additional features.