Cancelling this 2023.2 tech release issue since the support for this release has come to end of life. Cancelling this 2023.2 port case does not affect any LTS or Unity 6 Beta/Preview that remain open.
Due to 21LTS being near the end of it's lifecycle we won't attempt to port the fixes we've done in 2023.X lifecycle this far back.
Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Scenes/SampleScene” Scene
3. Select the “Rigidbody other” GO in the Hierarchy window
4. Observe the “Fixed Joint” component in the Inspector window
5. Enter the Play Mode
6. Observe both the Console and Inspector windows
Expected result: The “Connected Articulation Body” value is removed
Actual result: Error is printed out: “A joint can't connect the body to itself.”