With the recent updates, there is now some overlap with the UEFI Secure Boot guide. I'm not sure the current state of Secure Boot is useful for non-dual-boot systems, considering the feature loss and the lack of additional security due to buggy kernels and permissive signed bootloaders from other vendors. Perhaps merging the UEFI Secure Boot guide into the multiboot guide makes sense?
There was some discussion about this, but I didn't follow up here, apologies. The UEFI Secure Boot Guide is a detailed technical reference, while I'm targeting the multiboot guide at new users, common issues, and procedural aids. A lot of the content you're referring to should go to the UEFI Secure Boot guide, or is already there... but a merge would be too much scope creep. I'll use this bug as a TODO for moving the more dry content out of the multiboot guide.
I'm closing this bug as part of a Bugzilla cleanup effort. The most likely reason is that the bug has been opened either against a component we no longer publish, or against Release Notes for an EOL release.