I have a Mac mini which is stalling during boot. I have been trying to boot it to recovery or diagnostics mode, but run into an unexpected problem.
The keyboard I'm currently using with it is a Corsair K95 Platinum RGB which includes a lighting controller. This means that the keyboard has a short startup time, only a few seconds, but enough that macOS apparently does not allow it enough time to start up between the USB initialization cycle and the deadline for detecting the startup key presses.
I then tried again by attaching a second keyboard, but again the system would not respond to startup keys; the documentation is silent on the behavior of startup keys when more than one keyboard is connected or on how priority is determined.
I was eventually able to get a startup key to working using an ancient keyboard, but I would not like to be stuck without a keyboard that cannot do this.
What are the requirements for a keyboard to be able to invoke macOS startup keys?