Installing LineageOS 17 Android 10 on Pixel

https://forum.xda-developers.com/pixel-xl/development/rom-lineage-17-0-pixels-marlin-sailfish-t3971039

Download twrp from here
Download LineageOS 17 from here

Boot phone to boot menu then fastboot twrp

sudo fastboot boot Downloads/twrp-3.3.0-0-sailfish.img

Wipe to factory defaults

Side load LineageOS Android 10 from the Advanced page on TWRP

adb sideload Downloads/lineage-17.0-withMTG-20191217-UNOFFICIAL-sailfish.zip 

Reboot and setup.