I guess something like that: https://tpm2-software.github.io/tpm2-tss/getting-started/201...

Basically TPM includes key that's also signed with manufacturer key. You can't just extract it and signature ensures that this key is "trusted". When asked, TPM will return boot chain (including bootloader or UKI hash), signed by its own key which you can present to remote party. The whole protocol is more complicated and includes challenge.

Tpm isn't designed for this use case. You can use it for disk encryption or for identity attestation but step 1 for id attestation is asking the tpm to generate a key and then trusting that fingerprint from then on after doing a test sign with a binary blob. The running kernel is just a binary that can be hashed and whitelisted by a user space application. Don't need tpm for that.