If you're looking for a new official rom to flash, you should probably try system76 directly. https://support.system76.com/
If you want to build, flash, and debug the rom yourself, I'd recommend joining the #coreboot IRC channel and starting a discussion there. https://doc.coreboot.org/community/forums.html
Martin
Apr 11, 2023, 14:08 by coreboot@coreboot.org:
Please tell me who I should contact if the following support question should be directed elsewhere. I have a System 76 computer with coreboot installed. A fine print error message flashes that an "overflow" is detected and I think the file path has "grub" in it. Brief flash, can't see. Is this the boothole vulnerability? It is in the firmware or coreboot, not on a disk grub. I have multiple OS and the message appears independently of loading a particular hard disk, although I have Fedora with the community copr installed on my primary disk. Thanks!