[Google Pixel 2 XL Questions & Answers] simplepinoi177:
1) The reason for this is Google had an exclusivity contract to sell through the US cellular company, Verizon; much like the original Apple iPhone did (at first) with AT&T. And, for reasons that are most likely stupid, foolish, and unconvincing in its justifications, Verizon locks their device's bootloaders. So, not that it's "locked" or "unlocked" in terms of carriers, but more-so whether a device is "locked bootloader" or unlockable because it was purchased from Google (or elsewhere, but at least originally Google) and not from Verizon. If you're wondering further, getting it from Verizon would allow Verizon subscribers and customers to be able to "lease" and pay the Pixel off in increments with their usual cell phone bill; but it's not all too exclusive because Google offers to lease if you purchase from them also! The only caveat is you have to pass a credit check when leasing from Google; but, then again, you have to pass a credit check when signing up for a Verizon cell plan as well!

2) So, with my limited understanding between the difference between just a regular "unlock" and an "unlock_critical" is that it might be that a regular unlock allows you to get a R/W access (root access) to the various vital partitions (i.e. system, data [not to be confused with userdata], even boot to a degree) while unlock_critical allows you to straight modify and replace partitions (i.e. what would've been the recovery partition [but now there's no such thing and recovery just resides in the boot partition], the whole system & data partition to have/run custom ROMs, bootloading screen, etc.). But it all is rather convoluted that Google probably agreed and, so you can/should be aware, they updated things within the past few months (I'm guessing June or July) where they rid the need to "unlock_critical" and bootloaders that are newer than a certain point/month no longer needs that fastboot command to unlock the bootloader and everything else in order to flash custom anythings...

3) Okay, so here's a very tricky thing to this.... Technically, yes you can relock the bootloader as well as there have been many who have successfully done so;

BUT

there are

so many more

that have

COMPLETELY

and permanently bricked their device attempting to do so and most (if not all) the experts here would advise anyone to just leave well enough alone. But, if it is insisted and must be, the way to do it is to remove all Magisk modules (because, for whatever reason, these modules can survive a complete flashing of a Full Factory stock image), run a Full Factory image where the flash-all command is left intact (meaning “-w” is unedited; I’ll go more into this later), running it through the initial set up process, then (for good measure, this step might not be at all absolutely necessary) switch slots and run the flash-all command on the other slot, running the initial set up process again, then rebooting to Bootloader Mode and running the fastboot locking command, then unticking (if wished and insisted) unticking the OEM unlocking. Again, a word of warning, that so many have relocked the bootloader and unticked the OEM unlocking which allows the unlocking of the bootloader, then find that their device goes into a bootloop; and since they had just locked the bootloader in 2/all different ways, it leaves rescuing the device with all but the fewest options – usually because it’s forgotten in one way or another returning all of the device back to stock.

If anything, what has been said around these forums is that, if returning to Google, there hasn’t been an (proven) instance that Google refused to repair/replace it because it had its bootloader unlocked. But it’s usually for that fear or re-selling the device in which this is usually sought; but in most (if not all) cases (the experts here figure), having the bootloader unlocked would be refused or looked down upon.

4) So, most of what you assumed here is correct; but may be a bit misguided due to not knowing some things – which, of course, can be expected since you had just said you just moved to this device from a totally different manufacturer (Sony). If you are rooted (Magisk), there is absolutely no way you can update via the regular System Update from an OTA from within the Settings in the OS. And even having just an unlocked bootloader will cause OTAs to not work -- but there are conflicting reports stating differently, but I, personally, am under the understanding that even at that point you cannot.

But here’s the key thing; there really isn’t any reason to install updates by download and using OTAs anyways. Most (if not all) the experts here actually forego the OTAs and merely download the Full Factory stock images from Google’s Developers website and flash those. Here’s the reason; in the “olden days”, flashing a stock Full Factory image would erase absolutely everything and return the device to a complete factory state. But Google, in their “infinite wisdom”, allowed it to be possible to flash this but still withhold and save/keep all of one’s apps, settings, and data – essentially leaving both device data and userdata untouched! This is achieved by simply editing a batch file called “flash-all.bat” (or “flash-all.sh” for Linux and MacOS) and removing the 3 characters “-w” (3rd character would be a space “character”) from within its code. In this manner, OTAs can be considered a “dirty flash” because, while a Full Factory will completely overwrite (I could be wrong, but I believe it erases and formats it) the system, radio, bootloader, boot, etc., which would/should take care of any erroneous bugs or glitches, while OTA’s do not necessarily do this and just “modifies” the existing data; and therefore bugs and glitches may still remain being more on the root of things and/or OTAs would just modify “on top” or elsewhere where those glitches may reside.

And in either/both cases, one would still be required to reflash/reinstall everything root.

But, if insisted, there are multiple methods to achieve a state where you can run an OTA; either downloading an OTA image from Google and manually flashing it (“sideloading”), or unrooting temporarily to be able to use & download the regular System Updater (can be found

HERE

: https://github.com/topjohnwu/Magisk/blob/master/docs/tutorials.md#ota-installation under the “Devices with A/B Partitions” which is my preferred method if I was to do this sort of thing, but I have never done this so I’m unsure if it even is successful in our device). I even wrote out an in-depth and step-by-step guide, but it is rather convoluted and was written in the beginnings of our taimen and there are most likely more updated methods now; but if you want to check it out, you can HERE.

But, to answer your questions directly; No, flashing the stock image will not allow you to user the stock System Updater; although there are conflicting reports, I am under the impression that anything other than a locked bootloader will allow the stock System Updater to work.

5)More correctly, you boot into “Bootloader Mode” to be able to use the “fastboot” commands. And no, you do not need to permanently flash a custom recovery (TWRP), a custom kernel, or anything else to achieve root – although I do highly recommend it – as you can temporarily boot into TWRP (by downloading the TWRP image file (*.img) and install Magisk in that manner – I do not suggest you root/install Magisk using the app. Other people have had success, but many (most?) have issues that you wouldn’t run into if you installed it via TWRP – but here’s a key thing; no matter what you intend to flash and install, unless you need to have root for it to already be installed, you should always flash Magisk last. Moreso, as the great Az Biker of ‘round thes’ parts greatly suggests, you should even reboot to bootloader after each and every flash separately. Explanation is, for whatever reason and even though many claim to be able to “detect” and modify their flash for an already modified boot and dtbo (where modifications must happen for root access), most don’t play well with Magisk and Magisk must modify the boot and dtbo after all other modifications or else problems can arise (or at least it has for me).

Just keep these things in mind, but, for the most part, your “order” of things will do well enough. Again, just keep in mind that if you are going to install a custom recovery or kernel, try to do that before Magisk as well as if you can avoid it, don’t use the Magisk app to install or manually flash any boot.img if you can help it.

6)No, you don’t have to stick to a specific version; it might even be suggested to update it stock before doing anything. BUT (of course there is a caveat), consider this; many things (especially anything root and specifically TWRP) aren’t really “playing nice” with Android Q/10; so, if you update and go to the most up to date, but don’t wish to run into those glitches/bugs and wish to “hold off” (like I am, actually and for the same reasoning), then of course you should only go up to August (I believe that was the last before the upgrade to Q/10) Full Factory.

7) There are many great resources on the information on having the 2 different slots; I apologize if I can’t recall where I even saw them – other members (maybe an RC or Mod even) input a URL to read and I can’t for the life of me recall where it possibly could be. But, for the most part, you would really only run into identifying and manually changing to a specific one if you were attempting to rescue or deeply modify your device; I can say that me and the great [MENTION=4670411]Az Biker[/MENTION] have never felt the necessity to manually change or choose a certain, specific slot. And, my guess, is that, because the coding and flashing output when running the Full Factory states something about “system_other” or a “system_b”, but while the main system can be close to 3GB, the system_other is closer to 300MB, and that boot, dtbo, vendor, and something called lafb has a “_b” partition, I’m thinking it’s something as a safety or backup, maybe something like what used to be in old laptops a sort of RAM to help load things up faster. In any case, it seems that going from one to the other, a to b or vice-versa, doesn’t seem to be too key or much of a hassle, so….take that for what you will.

Alright…hopefully I was able to answer all your inquiries. And, if you have any more, please feel free to ask them…that’s what we’re all about here. And I know I can run on and get wordy, so thank you for bearing with me with all of this.

I mean, it’s really good to have a user/member who really does their research, reading, and due diligence before getting into their new device; there are so many instances here and in my own experience where the “…if I only knew that beforehand…” would be supremely helpful, and supremely easier on everyone else! So that’s to be commended and reinforced…!

Hope this helps and welcome to your Pixel and this taimen forum!