It worked for me using twrp from https://forum.xda-developers.com/p10/development/recovery-twrp-3-2-1-0-emui-8-0-4-04-2018-t3773449 and magisk 16.0 on oreo firmware.
Confirm working for me on L09C432 using stock oreo firmware. '/data' seems to be decrypted and also 'adb shell' was successful.
I had to use adb reboot recovery though, Vol+ on bootup always takes me to eRecovery (which I assume is a good thing).
Edit: One thing I noticed is that this...
Is there a way to retrieve the exact name of the installed stock firmware? For my VTR-L09C432 there are multiple versions listed (like 360, 365, etc). Also I am wondering what's the difference between FullOTA-MF / OTA-MF / FullOTA-MF-PF, etc.
The P10 is now fully supported by Phh-Treble, according to the list of supported devices in https://forum.xda-developers.com/project-treble/trebleenabled-device-development/experimental-phh-treble-t3709659