Single user mode comes up with wrong boot disk
I was just working on my 2011 mbp. I think the solution is to downgrade it to Sierra. I was happily on OS Sierra doing my work, but my bloody itchy finger clicked install, and I had to redo the kernel stuff, but it still didn’t boot.

I took out my hard disk and booted it from another MAC, and it worked perfectly. So my Guess is the the kernels we’re looking for some hardware that the mac doesn’t have, so instead of figuring that out, i’lol got back to Sierra.

Oh, to access csrutil, I used cmd-R from my other machine, and opened terminal to disable it.