Seems like the “faill installer” do not use the right process that is particular for this device, please follow official instructions (you do not have to boot to recovery, all is done throught “fastboot” in bootloader mode)
Install /e/OS on a Google Pixel 8 - “shiba”
Note :
- as your bootloader us already unlocked, go direct to the “Installing /e/OS” step.
- If you use windows you could face a driver issue [Solved] Windows does not see my phone in Fastboot mode