It seems that PXZ is a proprietary format, which means you need the original software to reliably convert Pixlr Zipped Layered Images directly to JPEG Images(.pxz to .jpg conversion). It is quite unlikely that you will be able to finda third-party solutionfor such conversion.
UsingPixlrwill allow you to export its PXZ images to numerous graphics formats, including JPG.
Keep in mind that since 2023 only a limited number of exports is allowedwithout having to subscribe for Pixlr's service.