Success! After wrangling with radeondrm/EFI issues, I finally managed to get 6.3 running on my old iMac with multiple monitors fully supported (thanks to some manual modeline work with cvt and xrandr)

Legible screenshot

A Mastodon instance for maths people. The kind of people who make $$\pi z^2 \times a$$ jokes. Use $$ and $$ for inline LaTeX, and $ and $ for display mode.