You may have come across this already -- and if you have, you are on the right path. Here is a solid list from the coreboot docs on mainboards they support.

You should be able to derive a few vendors from this list, as well as compare any possible candidates you have found to it. Some vendors on this list produce hardware that is Linux-forward, such as System76 and Purism. Linux-forwad vendors are good place to start.

System76 has laptops and small profile desktops, servers, etc. Purism has most of that, as well. Both are gonna be a little pricier than a typical vendor, but the hardware -- and their respective missions -- are worth it if you have the means. I have owned and / or used PCs from both these vendors, and they have been quality.

Otherwise, that linked list above will be helpful to determine if what you are researching has a mainboard that works. Best of luck!

i use libreboot with a samsung chromebook, running postmarketos.  works fine, no need to fiddle with it.

I am not using them myself but I have heard that some ThinkPads support Libreboot. Also, System76 sells laptops with Coreboot.

I don't think choosing a particular Linux distro matters with them.

Libreboot is amazing. But unless you are technical or have someone technical in your life. It isn’t something that you need to deal with. It basically works and you can ignore it exists.