[Google Pixel 2 XL Questions & Answers] arismelachrinos:
Any help is greatly appreciated, I have no experience with Google phones, I was years into Sony.

I have just bought a Pixel 2 XL from a local shop in Greece, and of course, I want to root it and be able to install custom roms etc.

I have a few questions that I am searching everywhere recently and I would really appreciate if someone can make it clear to me:

1) I have read that you have to buy your phone from Google so you are able to unlock it? Can someone explain this to me? (My phone is not a specific carrier) How do I know if I am able to unlock my bootloader?

2)I have flashed roms and kernels in the past on my Sony phones, however I haven't really messed with the bootloader other than just unlocking it in the beginning. So now on the Pixel 2 XL I am reading so much about the unlock_critical vs the normal unlock, and I can admit I cannot understand the difference. Why does someone want to flash a bootloader? ( I do not understand what does "flash a bootloader" mean)

What I want to be able to do is flash custom roms, flash factory images to revert back to stock whenever I want, flash custom kernel, flash stock kernel, make a nandroid backup with twrp and restore a nandroid backup with twrp. That is all I want to be able to do without facing any errors with the bootloader,so do I need the unlock_critical ? And why?

3)If I unlock the bootloader with any of the two ways, am I able to re-lock it like nothing has happened? For example if the screen has dead pixels for some reason and I want to send it back for warranty but the bootloader is unlocked, can I lock it without it being logged? Or once unlocked, there is no going back to the warranty by re-locking? On many Sony phones we could do that.

4)If I unlock the bootloader and install TWRP I read that I will not be able to receive official updates from settings any more (OTA):

"NOTE #1: If you have mounted /system as rw at any point (like in TWRP), you must upgrade using the factory image method. OTAs will fail because they cannot verify the integrity of the disk since its verity data has been changed."

My question is, if I flash a stock image, does that get fixed? ( so if I flash 8.1.0 stock manually, will I be able to get an official update e.g. 9.0.0 from settings?)

Or if I just grab the stock boot.img of my current version of android and flash it with fastboot, then will I be able to get official updates from settings normally again?

5)Can I do the following on this order? :

Enable USB Debugging and OEM Unlocking

Unlock the bootloader (either critical or normal, whatever works)

Boot into Fastboot

Boot the twrp image from fastboot to the device

Flash the twrp zip to the phone to install TWRP

Flash the magisk zip so I root the device

Reboot and everything works? (Or do I need a custom kernel for TWRP or Magisk to work?)

Is there any issue you see with the above plan of mine?

6) Before I tweak my device in any way, is it okay if I update the device fully? So can I install any update available (OTA) and then unlock the bootloader and root etc? Or do I have to be on a specific version and not on the latest?

7)I have read something about 2 different slots on some flashing forums here, slot a and slot b, but it is not clear to me what that is. Does anyone know what that is? At which point may I face this?

Thank you very much.