This sounds like a lenovo machine. Or something with a similar MOK enrollment process.

I forget the exact process, but I recall needing to reset the secureboot keys in "install mode" or something, then it would allow me to perform the MOK enrollment. If secureboot is greyed out in the BIOS it is never linux's fault. That's a manufacturer issue.

Apparently, some models of Lenovo don't even enable MOK enrolment and lock it down entirely. Meaning that you'd need to sign with Microsofts keys, not your own. The only way to do this is to be a high-up microsoft employee OR use a pre-provided SHIM from the distribution.

https://wiki.archlinux.org/title/Unified_Extensible_Firmware_Interface/Secure_Boot#Using_a_signed_boot_loader

For that case, Ubuntu and Fedora are better because, per the Ubuntu documentation they do this by default.

On Ubuntu, all pre-built binaries intended to be loaded as part of the boot process, with the exception of the initrd image, are signed by Canonical's UEFI certificate, which itself is implicitly trusted by being embedded in the shim loader, itself signed by Microsoft.

Once you have secureboot working on Ubuntu or Fedora, you could likely follow these steps to enable TPM+PIN - https://wiki.archlinux.org/title/Systemd-cryptenroll#Trusted_Platform_Module

There might be some differences as far as kernel module loading and ensuring you're using the right tooling for your distro, but most importantly, the bones of the process are the same.

OH! And if you aren't getting the secureboot option in the installer UI, that could be due to booting the install media in "legacy" or "MBR" mode. Gotta ensure it's in UEFI mode.

EDIT: One more important bit, you'll need to be using the latest nvidia drivers with the nvidia-open modules. Otherwise you'll need to additionally sign your driver blobs and taint your kernel. Nvidia-Open is finally "default" as of the latest driver, but this might differ on a per-distro basis.