Free and Open Source Software

why would something have to be closed source in order to optionally provide secure boot? Couldn't you provide the secure-boot-enabled binaries in addition to the source for everything except the boot keys?

This is also something I don't fully understand. Unfortunately it's not easy to find what the requirements are to get a bootloader signed by MS. It's possible I'm mixing up these requirements with requirements for something else that requires a NDA, but it's really not that simple to find the requirements online.

It's possible that the latter is actually the case and it's not secure boot that requires it to be closed source. It's also possible I'm entirely mistaken and they don't need to make it closed source at all. I wish TrueNAS would give more details why it needs to be closed source - whether it's due to a NDA or whatnot.

Self sign doesn't defeat the purpose

The whole point of signing is that the BIOS can verify that the bootloader is legitimate. For a local Arch install, it doesn't matter because Arch doesn't distribute signed bootloaders and the environment is wholly personal. TrueNAS sells products and services though, such as enterprise-level support. It isn't just something used in home labs. Their customers may require things we do not, and secure boot support appears to be one of them.

Self-signing to work around the idiotic restrictions Microsoft imposes to get it signed would be one way to do that, but then the software is essentially acting as its own authority that it is legitimate. Customers would realistically rather the bootloader's signature is valid with the built-in key provided by MS since it means that MS is confirming its validity instead - not exactly a name I would trust, but I'm personally not a TrueNAS enterprise customer either.

You can use self-signed keys.

It's basically like saying you can trust your own certificates used by TLS on your own machine rather than going through a CA, but realistically businesses would rather use a CA.