So far 230 mb’s supported, including some sandy and ivy bridge and some phenom boards https://www.coreboot.org/Supported_Motherboards
If you have one laying around it might make a fun project.
Please note, I know zero about this and I can barely operate the computer they put in my truck, but it kinda looks cool, might even be fun to try on an old board I yanked from an emachines 1300
Coreboot has been around for a while and is used on expensive chromebooks. it’s nice but it’s not something anyone can just install like a Distro. it requires supported hardware. the Coreboot team has released a list of devices it supports it on but it’s not worth the hassle doing unless you buy a laptop that already has it.