Microsoft even has their own Rust project for UEFI.

https://microsoft.github.io/mu/

Already today you can remove the Microsoft keys from most mein board's UEFI and enroll your own. You can perfectly make your own UEFI implementation without Microsoft.

Most of the top contributors are @microsoft.com so I would say it's a bit more than just "in the loop".

If you want to implement UEFI secure boot and verify existing signed objects then you need to incorporate Microsoft-issued certificates into your firmware, but that's very different from needing Microsoft to be in the loop - the certificates are public, you can download them and stick them in anything.

It's not that Microsoft controls the issuance, it's that their keys are pretty much guaranteed to be installed and thus getting your keys signed with their CA means you can use the pre-existing trust roots.

They are also the one party that is forcing freedom-enabling but formal standard breaking ability of resetting Platform Key, because Microsoft actually documents (or used to) a process to deploy systems signed with your own key as part of the highest security deployment documentation for enterprise customers

Open as in "open for business".