Not sure why this page says Ubuntu won't work. MrChromebox's firmware just turned it into a regular UEFI computer. I've had Ubuntu Mate 22.04 working on a Chromebook just fine.
> Ubuntu and Ubuntu-based distributions, such as Mint or ElementaryOS are unsupported.
Do you think it's related to the kernel version?
> Only Linux kernel 6.1 LTS or newer is supported.
What kernel version do you get?
Mint and Ubuntu LTS ship with a 5.x kernel at the moment, so that may be the problem. Normal Ubuntu is updated enough to work, but many people will probably prefer the LTS release lest they need to update every 9 months.
You would want to flash a Full ROM (UEFI) which will then easily support any regular Linux distro.