I flashed PixelBoot's unofficial LineageOS 17.1 on Nexus 6P, however I failed to root it.
First I tried flashing Magisk-v20.4.zip, which failed w/ "cannot mount /vendor" error. Here suggests I should upgrade TWRP to a "Treble compatible version" but my TWRP is already the latest 3.3.1-0.
Secondly I installed MagiskManager-v7.5.1.apk to see if I could use the "patch boot.img" approach. But it kept "checking for updates" till the end of the world, not showing the "install" button at all. I should probably opt out of the canary channel, however I am already in the stable channel.
Thirdly I looked for LineageOS's su addon zip. Unfortunately they offer that kinda thing for 16.0, 15.1 and 14.1 only.
As the last resort I flashed SuperSU-v2.82-201705271822.zip and installed supersu-2-82.apk. But the latter just fails to detect the former and refuses to work.
How am I supposed to root my phone?
It it because of the incompatibility between Android10(LOS17.1) and TWRP?