> any ARM system

If you are talking bare metal rather than Linux support, many M-core MCUs are easy, and some of these (e. g. STM32H7) actually have usable 1995-level desktop performance sans MMU, ergo enough for many things that aren't web browsing. It's A-cores that's closed, because vendors have zero incentives to open them up and because the whole thing is a heap of Synopsys modules ducktaped together - and Synopsys has an less incentive to open up. And then of course, there are GPUs, that's not well supported even on x86. Video out - yes, you get it with UEFI GOP, but usually no multihead. You also get it on many ARM SoCs - the video output generator is sometimes documented, it's accelerator/compute that's universally closed.