By enabling this feature, the Record Finder will be hidden in the form unless the user filled up the conditional linked record filter. To find this setting, you need to go to:
Form Fields
Click on the linked record field.
Filter Records section
Find Conditional linked record filtering fields
Click on the filter field that you want to be required
Turn on the toggle: Hide the linked records if this conditional filter is empty.
The user can still create records in the linked records field regardless if the required conditional filter is populated or not.