Yes, thanks to Geenyous1 on another thread, I used a patched boot.img to root my OP6 without TWRP.I believe so. When I attempt to boot twrp-3.4.0-11-enchilada-Q-mauronofrio.img (as of now most recent), I get a Qualcomm crashdump screen:
QUALCOMM CrashDump Mode Attempted to kill init! exitcode=0x0000000b complete_and_exit
If you're just looking to root your device in the meantime, before a working version of TWRP is released, there's another way I discovered today.
Follow the instructions in this comment: https://forum.xda-developers.com/t/guide-how-to-root-oneplus-nord.4139411/page-11#post-84858219
but instead of using a Nord build, use the appropriate OxygenOS build that you currently have installed. (At the time of writing, the most recent version released to OP6 is 11.1.1, which you can find here: https://www.xda-developers.com/oneplus-6-6t-oxygenos-11-1-1-1/
If you don't have Magisk installed, you can get it here: https://github.com/topjohnwu/Magisk/releases
Things are changing with the advent of project treble and seamless updates. OnePlus will no longer release ROMs flashable via stock recovery (with twrp is possible but not recommended). The updates will be done on the slot not used for example...
However, I dislike A11 so much I might go back to 10.3.12. Can't uninstall Google apk's from system /product using Root Explorer anymore, and that's the main reason for me rooting.
Thanks for your response.