Here's a video: https://www.youtube.com/watch?v=fZ6z_-jO5UY
The Kobo runs Alpine Linux natively with a boosted-up kernel (although v184.108.40.206, and very difficult to upgrade) including SquashFS support, FUSE, kexec, etc. The main GUI uses Qt 5.15.2 for graphics rendering, which is very nice to work with.
The software is automatically started at boot with a daisy-chain mount sequence (update files are squashfs images, so I have to mount them to use the software) and it interacts with various parts of the OS.
It includes a Diagnostics mode, which can be booted up by sliding the power key, which the initrd detects in the first 3 seconds of boot. You can do factory reset/restore and update the software in it.
More details and download are available here: https://www.mobileread.com/forums/showthread.php?t=337972
I hope you enjoyed it! 😀