tested with thinkpad x1 carbon gen 5 and openbsd 7.7.
this can brick your thinkpad! proceed at your own risk.

update thinkpad bios and logo

prepare bootable drive

• plug in usb drive as sd2
• all data on sd2 will be erased!
• run bios.sh

# ftp -o - https://romanzolotarev.com/tp/bios.sh | sh -s sd2

bios.sh downloads an official bios update image, installs geteltorito to convert .iso image to .img, writes it to the usb drive, and copies logo.gif.

reboot and flash bios

• boot usb and follow prompts

image: thinkpad boot screen displaying a custom logo.