So I guess this is a tip for anyone needing single user mode, you may need to use OEM wired Apple USB keyboard to do it.
Good to know. However, I've used OC to access single user mode a few times, and it has worked fine with an Apple Magic Keyboard.
I've noticed at times recently when I boot into recovery or backup partitions my wireless keyboard and mouse don't work, even if I plug them in to attempt a re-pair. I have to keep the keyboard plugged in and rely entirely on keyboard shortcuts to get around. I thought this was an issue with my cMP or the partitions themselves, but it sounds like it might be an OpenCore issue?
I've experienced this too, but I think even before OC.