So I don't really need to have a wired keyboard on hand when starting the iMac in other bootup modes. Today I learned that if you connect an Apple Magic Keyboard 2 to the Mac via a Lightning cable it is still fully usable. In fact, the formerly wireless keyboard becomes a wired keyboard & it keeps charging. Other startup modes such as Safe Boot or booting from external drives or the recovery partition work fine, too, as long as the keyboard's power switch is at the "on" position. It still charges even while in use.