The minimum confidence level is checked when mapping each matching element (key-value pair). This uses a new global (system-wide) property:
ai.transformation.aiTextract.keyValueSet.minConfidence
This property has a default: 0.7 (i.e. 70%) unless overridden for a specific key/value mapping.
You can add an optional confidence field for each key in the property mapping configuration file to override the global configuration. See example in Custom AI property mapping.