It didn't work out as I have lost the root, while Magisk is still installed.Bluspark TWRP 9.116 has been available for a while, I have had it installed on my OP6 phone for the last few OOS updates (10.3.11 included) while following Section B instructions, and nothing has gone wrong. Also, Magisk 23 is available and I have had it installed since it came out.
No idea whether things will work with the older versions you have, but you might want to try to update Magisk and Bluspark TWRP before you install 10.3.11.
Now it asks me to patch the stock boot image.
Maybe can u upload this for me?