You're right, that's smaller. I think I was confusing the DS and the "Game Boy Advance", because I was thinking of a machine with a few hundred K of RAM. The GBA is a 16MHz ARM7TDMI with 288KiB of RAM, not counting the 96KiB of VRAM; the Nintendo DS's main CPU is a 67MHz ARM946E-S, and it has 4MiB of RAM.
As for what you're more likely to find in usable shape in a hypothetical collapse scenario, it probably depends on what kind of scenario you're talking about. Certainly vastly more Chromebooks exist than Suns, but the Chromebook's SSD only has a few months of data retention, so you probably won't be able to get it to boot if it's been sitting around unpowered for many years. All the Sun SPARCs are going to be in non-working order because their IDPROM batteries will have died, but some older 68000-family Suns like the 3/60 I theoretically still have are probably okay, because their IDPROMs are actually PROM rather than battery-backed RAM.
(Of course you also have to worry about capacitors drying out.)
What's vastly more common than Chromebooks, Suns, or GBAs, though, are Flash-based microcontrollers like the AVR family and 48MHz members of the STM32 family. (You can probably salvage a couple out of the wreckage of the drone that killed your parents.) And those will probably still be in working order, unlike anything SSD-based. I don't think Uxn is a good fit for those chips.
In a multiple-centuries sort of collapse scenario you also need to worry about the retention time of the NOR Flash in these microcontrollers. Hopefully if they lose their memory you'll still be able to rewrite it, but if the manufacturers used Flash to implement some supposedly-read-only memory, they might not bother to mention it.
In the collapse scenario we're actually in at the moment, GBAs, Nintendo DSs, and Chromebooks are all immensely more expensive than such microcontrollers. That seems likely to remain true even after the PRC invades Taiwan in a few years.