OK, that helps: on my system
Information[ResourceFunction["SymmetricDifference"]]
yields as Function Location
LocalObject["file:///Users/myname/Library/Wolfram/Objects/Resources/\
4f3/4f3f7f00-c70a-455e-8bd4-1eaa2b455ae5/download/DefinitionData"]
...which is in a different folder than you found!
An aside: it's really annoying that while Information
works on the ResourceFunction
expression, neither
?ResourceFunction["SymmetricDifference"]`
nor
?? ResourceFunction["SymmetricDifference"]
works — each returning
Missing["UnknownSymbol", "ResourceFunction[\"SymmetricDifference\"]"]
which seems to be contrary to what the Documentation Center page Information
says in its Details section about the special input forms! This is either a bug in the version 12.0 updated Information
implementation or an error or omission in the documentation for it.