CA Easytrieve release 11.6 is compatible with z/OS 2.3 with one PTF recommended.
Here is the link for review under Support ONline for the z/OS compatibility:
Clicking on 'Additional Information' provides this information:
Please ensure product solution RO94347 is installed.
This PTF is needed if the CA Easytrieve programs have a CALL to the EZTPX01 module in them.