Black screen, unable to install

I was going to install Manjaro KDE onto my old iMac mid 2010, but ran into a problem. When I try to boot into my bootable usb, the screen simply goes black.

This isn’t the first time I install Manjaro on that machine, previously I successfully used Manjaro Architect… although, I DID have an issue: it turned out, as soon as the radeon driver started, it failed to determine where to send the output, so I had to put the following thing into a /usr/share/sddm/scripts/Xsetup file:

xrandr -d :0 --output eDP --crtc 1

This did force the X server to show me the login screen, and then I was able to successfully use KDE, but it rendered all tty’s unusable (black screen instead of a console made debugging way more difficult than it should’ve been), but I couldn’t come up with another way to tell the system about the DisplayPort issue with my hardware.

The old installation got accidentally wiped out :frowning:

So, Manjaro Architect at least presented me with the GRUB and so I could perform the installation, but when I try to boot into manjaro-kde-21.0.3-210428-linux510.iso I get a black screen right before I can do any further actions!

Does anyone know anything about how this problem could be fixed (I don’t have a second monitor, so I can’t use it to install Manjaro and then reconfigure the system to use the proper display)? And maybe someone could help finding a better solution to the problem of redirecting the radeon output?