first of all ... are you rly installing an old xposed framework from 2016? when installing magisk you don't need to install supersu at all. magisk app can handle su as well ..... best would be to flash an actual magisk and install the magisk app, then install xposed framework using the magisk app from the download section that fits to zhe sdk level of your android device.
I just switched from Magisk to SuperSU for a reason. My device (Sony Xperia M5) has got a kernel with a DRM fix that is not compatible with the latest version of Magisk. This means I will lose some functionality on specific Sony features (such as noise reduction on the camera). And Staying on Magisk v14 will mean some modules probably will not work for my device in the future. So all i want is to get systemless xposed to work on SuperSU, which currently results in the error messages as mention in my last post.