First,if your phone security patch is A.30 and up please downgrade your phone (A.17) specifically.
then install mtk-su from https://github.com/JunioJsv/mtk-easy-su
in magisk click modules and install ADB & Fastboot for Android NDK by osmosis
(since oppo a5s have no fastboot and you have to install it manually)
and click reboot.