Rooted the same way as always - took the boot.img from the installer package, patched in Magisk, flashed using fastboot.
No root. Tried multiple times, re-patched the file, even used different USB cable. Nothing.
Any idea what the problem could be?
Hello @Borpo, Welcome to the /e/ forum.
Read carefully the unclear Magisk instructions on GitHub…
For recent devices it have to be done using a different way…
Thank you! I see this method isn’t recommended on modern devices, which makes me a little cautious, since the FP6 is brand new.
Have you rooted a FP6 using this method? Or know a good place for me to talk to anyone who has?
No, only an old Samsung, flashing the patched-boot.img using TWRP.
solution here : Magisk root with /e/OS 1.9 impossible - #6 by julien.lvs
Yep, that’s the exact procedure I followed. No dice 
Edit - more complete description of my method for clarity:
1 - Extract the boot.img file from the installation file (in my case, here)
2 - Download the latest version of Magisk. Currently 29.0 is the most recent stable version, and the latest pre-release version is 30.1. I tried using each one on separate runs with the same result.
3 - Install Magisk on the FP6 and use it to patch boot.img. Put the patched image on my computer (laptop running Ubuntu, if it matters).
4 - Reboot to bootloader, run ‘fastboot flash boot [path to patched boot.img]’. The process appears to go fine, taking under a second.
5 - Reboot to system. Magisk and Root Checker both report no root.
Did you flash both slots ?
or,
Did you switch active slot after flashing inactive slot ?