[Samsung Galaxy Note 8 Questions and Answers] krabman:
Like many I spent time in jail waiting for my OEM unlock. How I spent that time was trying to work around not having root and it was a miserable failure. When talking about the need for root I think it's best that the conversation first be understood to be subjective. A person that doesn't do anything that requires root will feel that it is unnecessary, those that do will consider it vital as a means to get where they're going.

There are many, many, people who said "you don't need to do that" in regards to getting root on these devices who went down in flames. No timer on OEM unlock and not a big deal, you try again until you get it right. We get one try and getting it wrong means you have reset your timer and you're waiting a week. Wait that week and you get one try, failure means another week. A person can repeat that cycle as many times as they want, I'd suggest going all in the first time because no one knows exactly which steps are not needed yet although we have ruled a few out. One thing that is apparent is once you have the first rom install in the rest can be done following normal rom installation procedure so long as they're clean flashes. I haven't tried any dirty flashes but for the same rom I'm thinking it will work, of course when the time comes I might be proven wrong. I'm hoping someone else will get there first and I can take advantage of their experience.

That being said in general the process begins by flashing TWRP in odin. You must leave odin and go directly to TWRP, failure to stop the boot at recovery means a certain binaries error and a week wait. Once you are in recovery you must stay there until you have finished installing a rom that has been de-knoxed. Pay attention to holding the buttons on the phone while you start the TWRP flash as described in the TWRP thread. If you untick reboot in odin then the only way out is to hold volume down/ power which will tell the phone to reboot into system. You must then quickly switch to volume up/bix/power during a small window in order to get the phone to go to recovery. If you miss it nothing can stop the phone from continuing to boot and you have just got a week wait before your next try. If you don't untick restart you can try the same thing when odin automatically reboots the phone after the flash. If you miss it you will get the binaries error and be waiting a week. People have missed it both ways. There is a reason that the TWRP instructions specifically state to prepare odin, hold the vol up/bix/power buttons and continue holding them while you press the button in odin and keep right on holding those buttons all the way through until the phone boots into TWRP. This makes it a sure thing, the other way you may or may not succeed. Lastly we've proven you don't need to remove your SIMs on subsequent rom installs but it remains a question with the first install as there are conflicting reports. If it were me I'd pull them and not put them back until I was fully up and running on the other side. You will need to pull at least Sim 2 in order to put in the micro SD with your rom, verity, and root firmware for use in TWRP no matter what. Feeling frisky and you want to leave Sim 1 in then please report your results in the OEM unlock thread.

So... To install a rom you will begin by following the TWRP instructions to the letter including the format all the way through the process until the end. Some will say you don't need to flash the no-verity, ordinarily I'd agree with them as it is flashed as a part of both the SU and magisk flash but in this case we know that following those instructions in exacting detail works as a first step but not doing so has been a failure for many. Because few have followed the same steps plus or minus a detail from the known working method we don't know exactly which things are unneeded so if it's me I would just follow the known working method. As always those wanting to advance our knowledge by trying something else should report their results in the OEM unlock thread. When you reach the end of the TWRP installation instructions you will remain in recovery and flash your rom and then factory reset. Then flash either magisk or SU again depending on which rom and which root method you're using. Once root has been reflashed you can go ahead and boot to system. Finish the setup before you put the sims back in the phone.

There is a longer throw the kitchen sink method in the OEM unlock thread for those that wish to search, that is what I would do if I wanted absolutely no risk as it seems to work without fail. I've done what I describe here a good ten or more times now as I was the first reported rom install here using the first method and I've been flashing away since then and dropping some of those original steps as I went. I'm thinking it should work for others too but I cant prove it until someone does it. It may be you need the kitchen sink for the first flash, I simply cant say because I would have to go stock to try and I'm not harboring much of a hankering to do that. This being XDA and we being adults please understand that I'm sharing the information based on actual practice on my own phone but there is no guarantee. You make your choices and what happens, happens.