I have a librem 13, with pureboot/librem key. There are times that I would like to disable the secure boot feature so that when I turn the machine on it just boots without the key. But I don’t see an obvious way to do this in the boot options. Any suggestions?
Maybe I misunderstood your question, but to boot without the Librem Key you could just hit the “Default Boot” selection. You’ll just not verify that your device hasn’t been tampered with by the green blinking LED on the Librem Key. Still you could verify the device state by using an otp program on another device (like a mobile) if you initialized it with the qr code shown during setup of heads.
It is actually an additional layer of security for us that people often make misunderstandings like this 
Ok you can do whatever you want to pureboot even without a librem key. Just dont be scared by the red thing.