I'm not avoiding the answer, and I've answered your question more than adequately. It seems you want hand holding each step along the way. Are you perhaps unaware that the coreboot implementation is called verified boot rather than secure boot?
I've shown it's possible to flash hardware and have an entirely open source and auditable secure boot implementation which is better than your current solution in a number of ways. That was all I had a burden to prove, and I've met it.
If you want further help or convincing, I'd suggest interacting with an AI to get answers to your questions.
[1] https://doc.coreboot.org/security/vboot/index.html
[2] https://github.com/tianocore/edk2