I’ve always been a fan of extremely small Linux installs. Back when I first started using computers, I didn’t have access to great hardware. In the early 2000s I was using Pentium133 and eventually a Pentium III based system and I remember running floppy Linux (live boot off a floppy disk) and DSL (damn small Linux) in attempts to maximize the performance of the hardware I had.
Running Linux on a tiny ESP32 board just blows my mind!
It’s been done on a 8bit microcontroller, he did use a hack to get around the MMU, but you can run Linux on an Arduino
https://dmitry.gr/?r=05.Projects&proj=07.+Linux+on+8bit