Unlock Bootloader (classic method)

This might not work, google keeps patching this and unpatching it sometimes.

(last time it worked in july, but there's someone that did this recently)

Tutorial from https://forum.xda-developers.com/pixel-xl/how-to/how-to-unlock-bootloader-verizon-pixel-t3796030

Remove Google account and any kind of screen lock (fingerprint, PIN, pattern, etc.) from your device. Quickest way is to just factory reset the device

1. Eject sim card from your device.
2. Reset your device. In setup wizard, skip everything you can. ESPECIALLY: DO NOT CONNECT TO WIFI
3. DO NOT add fingerprints
4. DO NOT add a screen lock.
5. Enable Developer Options
6. In Developer Options, enable USB debugging.
7. Connect your phone to PC
8. Check the box to always allow your PC
9. Open a command shell and run the following command: adb shell pm uninstall --user 0 com.android.phone
10. Restart your device (using the power button).
11. Connect to WiFi
12. Open Chrome and go to google.com
13. Go to Developer Options and the option to enable OEM unlocking should be available.
14. Enable OEM unlocking.
15. Reboot into bootloader and run fastboot oem unlock
16. Reboot, and enjoy your now unlocked bootloader!

NOTE: You may need to run the factory reset twice in a row, and reboot twice after step 8.