This may have been true at some point... in the 90s? I'm not sure if it actually was even true then. In any case, it isn't true today:

https://minifree.org/product/libreboot-t480/

https://pine64.org/devices/

https://puri.sm/products/librem-14/

https://www.raptorcs.com/TALOSII/

https://frame.work/ie/en/products/laptop16-diy-amd-7040

https://www.olimex.com/Products/DIY-Laptop/

https://shop.mntre.com/products/mnt-reform