Source: https://nectivdigital.com/blog/how-to-mine-google-search-console-for-conversation-data-regex-included/

1. Go into Search Console Performance > Search Queries
2. Select Add Filter > Query
3. Choose “Custom Regex”
4. Enter the below regex. The result is queries with 15 or more words. Change that value as needed.

^(?:\S+\s+){15,}\S+$