[Google Pixel 2 XL Questions & Answers] simplepinoi177:
It’s really my pleasure! And I’m just as thankful that you/anyone would even go through the trouble of reading all of that…!

1) Thank you for the compliment

2)Usually, if your bootloader version is within a certain version – which you can find when in bootloader mode – then you either do or do not need unlock_critical. I can’t remember how many months prior to Android 10/Q, it was within 6 I believe, so any bootloader version from 5 or 6 months ago to now, and obviously if you’re on 10/Q, you would not need to run the command unlock_critical. But, if anything, you don’t have to have any fear of it, whether you need to or not, or don’t know your bootloader version, running the “fastboot flashing unlock_critical” when you don’t need to will just amount to a simple error and nothing bad will happen. And if it does end up doing something, well, then that’s a good thing. It almost amounts to unlock_critical-ing twice, the second on will just state that it’s already unlocked and that’s it.

If anything, I believe I found the resource here from the great Az Biker: https://xdaforums.com/showpost.php?p=78908055&postcount=2843

If you are very curious, it should address much of what you’re seeking and/or at least point you to where you might find that information.

3) You’re very welcome. It really is a good thing that saves you in the future, and saves those who try to help some grief as well.

4) Thank you for the compliment.

5) I would say that the process you described is certainly doable, but is far from the best/easiest. From my experience helping many here on this forum, many bugs or things go wrong when loading the stock boot.img to the phone, having Magisk modify it, then getting the modified boot.img and successfully flashing it. More often than not, one ends up having a device turn into a boot loop and are usually forced to flash the stock boot.img and have to give it a number of tries.

The best way (subjectively) is to download the Magisk installation .zip. Then boot into TWRP (which doesn’t mean you have to replace the stock recovery since you can temporarily boot into it), and “Install” it using the .zip. Then everything is automated and done for you, if anything goes wrong you have an output log you can use to troubleshoot, but it seems best to leave it to the experts who created all this than us manually attempting to ourselves.

Oh and AFAIK this method still works on Android 10/Q as it has for Pie and Oreo.

6) I meant that, if you did not wish to update to 10/Q, then you shouldn’t do anything newer than from August’s security update/patch, since all the Full Factory images and updates are of 10/Q. But, if you go to Google’s Developers site, you’ll see that they pretty much list and make available all the Full Factory images ever published; to the point that there are some that go back to Oreo!

And everything you’ve said is understandable. And I kinda feel the same way. For me, in my humble opinion, it is supremely good idea to root and for whatever issues you get doing that, the returns are incalculable. It is most definitely worth it/rooting! The extra options and customizations and modifications all make it worth while and more! And, even if rooting gives the capability of rendering the device rather unusable, take confidence in that Google, in all their “infinite wisdom”, gave us “Bootloader Mode”…and pretty much, as long as you can get into Bootloader Mode and successfully connect to a computer, your phone would never be considered too far lost/gone. I’ve only witnessed that be opposite on less than a handful of cases.

But, most importantly, and if you have been in the rooting and ROMing game, you should well know this, but the most vital part of having root access is the ability to make the best backups! So, as long as you make sure to backup (Nandroid is best) and key times, running into some pitfalls here and there shouldn’t take you all the way out of the game….

7) Yeah…I mean, it is rather fascinating, and when up against an issue and you have an idea that deals with it, that’s when you can read up and learn about it and experiment I imagine. But for me and one of the great ones here in all of XDA, we’ve done all the custom ROM, custom recovery, custom kernel, Full Factory recover, root, Magisk modules, theming, Xposed, and countless other things, and all without the need to ever mess with manually or forcing an assignment between the two.

Again, it’s my pleasure. And if you any further questions or thoughts, bring them on! I’d be happy to address them…

Hope these are helpful….