@saley Thank you for reporting your crash. 5.9 hung on to an old version of libomp, which may be involved in this case. If you try a recent development build you may experience more stable multithreading as that particular library has been since upgraded. (Currently I am testing the metadata-exiv2 feature branch): https://kd6kxr.github.io/meta
For the sandboxed 5.9+ application bundles, options will be found in ~/Library/Containers/com.rawtherapee.RawTherapee/Data/Library/Application Support/RawTherapee5/config