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It has been introduced as beta in 2.21.1 - Release Notes#Version2.21.1 and as GA in version 2.24.7 - Release Notes#Version2.24.7
As with all "smart" fields in ConfiForms this field is about linking forms together, but with one important difference - it allows you to ADD new records into the referenced form directly and in "one go"
Here is what we mean