My 8-year-old’s computer is a Raspberry Pi 400, in fact. I’ve been looking for ARM devices that have accelerated AES (Raspberry Pi 4 doesn’t) so I can use full-disk encryption with them. There are a number of options, since ARM devices are starting to go more mid-range. The Orange Pi 5 Max and Ultra have up to 16GB RAM, as does the Raspberry Pi 5. Radxa has a page on running Debian on one specific board, they seem to actually not support Debian directly, but rather their fork Radxa OS.