Recovering from a true hardbrick (that is, can't even get to the bootloader) is not an easy task. It would likely require proprietary firmware flashing tools from Qualcomm, which they don't generally make publicly available. I'd be cautious about any site claiming to host those tools since, again, there isn't a legitimate source of the tools for users.
My honest recommendation would be to instead contact Google Support to inquire about an RMA under the Pixel 2 XL 2-year warranty.