The Query a database page was updated with additional information about the filter_properties query parameter.
When used with the REST API, this query parameter is passed as a string, like so:

https://api.notion.com/v1/databases/[database_id]/query?filter_properties=[property_id_1]&filter_properties=[property_id_2]

Notion Changelog: https://developers.notion.com/page/changelog#may-2---may-15-2023