In reference to the thread - https://community.oracle.com/tech/developers/discussion/2311406/logical-diagram-notation-information-engineering-notation, I have the same question. The Source Optional and Target Optional settings seem to continue to be reversed in the IE Notation in Oracle SQL Developer Data Modeler version 21.2.0.183 Build 183.1957. Checking Source Optional controls the optionality of the Target and visa versa. These display correctly in Barker and Bachman notations.
The above thread shows closed, but no pointers to the resolution.