Actually I am confused. I want to root the right way in one go. What you suggest I should do to remove TM logo and get "LOCAL UPDATE" option.At least for me, using those fastboot ROMs wasn't that straightforward. My issue occurred when I tried flashing directly to a global Android 11 ROM. The modem didn't work at all. I had to downgrade to Android 10 with MSM, then flash an Android 10 fastboot ROM, then install the OTAs up to the current Android 11 version. Everything worked after doing all that.
What you stated about root is correct. The patched boot image needs to match the version you have installed.
As you know I have 184.108.40.206.IN55CB OOS installed.
FYI, I also have a copy of the PATCHED boot image software build 220.127.116.11.IN55CB which I got from this thread.
FYI, I also have OxygenOS 18.104.22.168.IN21AA (AA = Global) which i found from this site https://www.thecustomdroid.com/oneplus-8-pro-stock-boot-image-collection/
What should I flash ?