I'm trying to install Ubuntu 18.04.1 LTS on a 2011 Mac Mini that's controlled by an Apple Wireless Keyboard and an Apple Magic Mouse. The installer boots into GNOME just fine, but neither the keyboard nor the mouse work in the graphical environment. Strangely, the keyboard works perfectly if I boot into the minimal "netinst" image and I'm able to install everything, but as soon as I reboot, I'm faced with the same problem: it boots to the GNOME desktop and neither the keyboard nor the mouse work.

How do I boot into the text-based installer if I have the official Ubuntu Desktop .iso? I've tried editing the kernel boot options in the pre-boot Grub editor but it still keeps booting into Gnome and rendering my keyboard useless.