It can be accessed under the Stores menu > Configuration > ElasticSuite entry > Behavioral autocomplete entry

behavioral-autocomplete

Parameter Default value Description
Enabled Yes When enabled, autocomplete box will suggest trending search terms. If disabled, autocomplete box will suggest matching search terms with the most uses. Elasticsuite tracking must be enabled in both cases.

If enabled, autocomplete box will display trending search terms like this :

trending-search-terms