Install hangs with gray rectangle accross screen

I’m installing on a 2010 Mac Mini, off of USB. Ubuntu 20.04 installs fine. I disabled "splash" and "quiet" in grub. I don’t see any error messages. The kernel boots and then hangs with a gray rectangle across a black screen. It takes up about 1/3 of the screen down the middle.

I’ve tried adding "vga=ask" "vga=1280×720" and "GRUB_GFXMODE=1280×720." None of those worked. I still get the hanging grey bar. My monitor is 4K.

Does anyone have some help with this one?

Thanks,

Kent