The authors of both this article and ssh-tpm-agent (disjoint set) really need to learn about pcrphases and the signing keys therefor: https://github.com/Foxboron/ssh-tpm-agent/issues/15

Do you have any more info you could add about that topic, or a direction to point me? As far as I know, (systemd-)pcrphase is for measured boot, but I'm not sure how that interacts with signing keys.

As someone who stores my SSH keys in my TPM, and has struggled with picking the right PCR values for Secure Boot in the past, I'm interested in learning more.