[Google Pixel XL Guides, News, & Discussion] Letitride:
Breaking news - I UNLOCKED bootloader, rooted & install Lineage OS V17 (Android 10 final build) on my OG Pixel (PVT variant). Here's my results, see screenshots & photo images taken yesterday ... woohoo. As always - please read, follow and give it several tries on your best efforts, and YMMV. Good luck.

One of the most useful aspect of having, owning & using the Google OG Pixel or Pixel XL after June 1, 2021 is the continuing support for uploading original photos via it to Google Photos for storage (until early 2022) without being counted against one's allowance, or having to pay more/extra for it. I do have Google One with 100GB shared among 3 accounts but ... Some of the "original" photos are precious & priceless memories of families & friends - I've sold my 1st. generation Pixel XL Google Edition earlier to move up to the 3a XL, but let's say, I do miss the Pixel's unique choices these days - thus, I picked up an inexpensive Pixel in good to excellent condition, battery life is average but otherwise great overall, supposed to be the Google variant, unlockable bootloader. Well, it was/is not when it arrived by postal package and my reaction was ---- (fill in your own words) knowing that it is a waste & going to need to return to seller. To make a long story short, I failed twice with previously outlined steps and ADB sideloaded, etc. etc. taking all the steps, no luck or success .... resigned to either use it as is, with stock rom or return/refund & go find another one.

"OEM Unlocking" option under Developer's option within Settings was greyed out, no matter what - was on the final OEM Build ... until

A word of warning, doing these could damage and/or brick your Pixel, and I am not responsible nor anyone else that wrote the steps & guides for the attempts/efforts to get the locked bootloader to somehow unlock, root & install your choice of custom rom, etc.

First, I follow the steps to factory reset, install ADB and sideload, etc. and re-install the zip file, reset & boot, initially without connecting to WiFi, enabled Developer's option, enable USB debug, and confirmed that both ADB and FASTBOOT options are working, that the PC (Windows 10 Pro, 64 bits) recognizes the serial number/device ID. Uninstall the com.android.phone via ADB before another reboot, connect to WiFi & open browser to google, open various websites and check the OEM unlock options, etc. - it was still no can't do. After spending all afternoon/evening, trying & waiting, cursing too, I gave up AND decide to sideload the final stock rom zip file again, and boot up to do the basic / regular setup, etc.

Well, after installing basic apps and setting it up for minimal functions, I went ahead to play with it. Well, I went back into Developer's setting and guess what, the OEM unlocking function is now enabled, no longer greyed out. Woohoo - joys, I went ahead to boot into bootloader/fastbook, and, unlocked it. The rest is history - after clicking the "warning" on screen. Lineage 17 (Android 10) is now installed, running, with pico gapps, and Google settings from a previously saved device and apps restored, up & running smoothly.

I did not insert any nano sim card (this will be kept & used at home and connect to WiFi only) mostly for uploads & cloud access.

To sum it, follow the previously documented steps to try and if it failed (most likely, it will ... just like me) then by the 3rd time, reset again but let the sideload rom/zip file install fully - boot up the stock rom, then, setup as usual, for a minimal one. Wait & let the rom settle & finished updating everything from Play Store, etc. - then, check again about the OEM unlock option (fingers crossed & good luck). If you are like me, the device will be fully wiped again as part of unlocking & factory reset, erasing everything - then, you are good to sideload Lineage and optionally, gapps, etc. and enjoy.

Any questions, feel free to ask and if I can help, will cheerfully do so. Have a great week ahead. It it works for you with a bit of efforts, thumbs up and if not, please share anyway. Good luck !! Next, going to upload photos at full quality/resolution (almost all are 12 MP or less in resolutions anyway) for additional "free, for now" secure storage.