Various Quicken programs allows users to exchange the data via Quicken financial data file (.qdf) and as such, it should be possible to perform qdfx to qdf conversion in the OS X version of Quicken. It is unlikely that any other software would be capable of this conversion.
Convert Quicken Essentials for Mac financial data exchange file to Quicken financial data.
We have found one software suitable in our database for this conversion.
Apple macOS / Mac OS X software - convert qdfx to qdf on OS X
Mac version of popular Quicken personal finance management software
Convert from qdfx file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.