I have rootet my Samsung J6+ (Oreo 8.1) with the latest TWRP from here and installed Magisk and Manager latest Version
It works for Rootchecker and some little Apps which need Root.
But TB and Links2SD do not recognize the given root-rights. Both apps ask for root, Magisk gives it. I see it in a short info-windows and in the list of apps with root-rights. But both apps tell me "No root".
This problem seem to be very old. I found many old threads. But never a working solution for today's android => 8.x.x .