I have been pointed to community/Heads Matrix room for help with this sort of thing: https://matrix.to/#/!BSPqgzeiCeaSBayTLM:talk.puri.sm
I am no expert on these matters, but I have been doing a lot of flashing, formatting, reinstalling, re-configuring, breaking (intentionally and unintentionally), fixing, etc. with Linux and my Librem. I am trying to learn a lot about these things, and I learn best by doing. This includes seemingly breaking PureBoot and recovering from a similar place to yours. I did what I write below, and it worked for me:
Since you can still boot using your normal LUKS passphrase, it should be safe to flash the normal core boot bios, which would strip out all of the heads bits. Information on that is in this discussion.
Once you have a “normal” boot working (power on, Purism logo, LUKS prompt, booted to system login or desktop), reset your Librem Key, and start the process over again: move your private keys to the Librem Key and your public key to a flash drive, flash PureBoot back onto the machine, and configure heads.