Comment 37 for bug 1980018

"What gives you that impression? What PCR do you see being extended by GRUB
with a hash of the initramfs when loaded?"

I found if I update initramfs on Ubuntu 22.04 then PCR9 changes.

I only tested this as below lead me to believe this was an intended behaviour:

https://uapi-group.org/specifications/specs/linux_tpm_pcr_registry/
https://wiki.archlinux.org/title/Trusted_Platform_Module#Accessing_PCR_registers
https://www.gnu.org/software/grub/manual/grub/html_node/Measured-Boot.html
https://github.com/rhboot/shim/blob/main/README.tpm

Hence when I read your original comment it left me wondering whether I'm misunderstanding something.