With the help of a friend, I librebooted my T420! I used a Raspberry Pi 4B and Pomona 5250 to flash the GRUB payload. It boots extremely quick now and just works. Despite the picture, I'm running the latest June 25th release but I put the old gnulove.jpg background picture on.
The only issue is when I reboot from Linux, my SSD isn't recognized until I power it off and back on again (cold boot). The folks in the IRC say it's probably a bug.
Overall, I'm happy with the state of my ThinkPad and it's running as much libre code as it reasonably can (but I still like having WiFi).
Yes, the ME is neutered :)