thank you! I think this is what needed to explore
It is not my level to edit these things, I'm just Linux newbie exploring the possibilities.
But I still can't wrap my head over dd not being able to wipe a storage device out, despite being described as a "low level tool that can write zeroes to targets" in the discussion I viewed online.
You can mount the efi partition, but I don't think you can usually mount the uefi or bios. I've only ever edited vbios, and haven't done so in quite some time, but I remember needing to clamp the vbios chip. Dunno if motherboards make their bios chips more accessible, but I kinda doubt it.
Some motherboard support starting bios/uefi updates from a booted OS, so there might be a vector to be found there.
Early true BIOSen were stored on EPROM, which couldn't be rewritten while on the board, so those were read-only.
Later BIOSen were often on EEPROM or other chips that could be reflashed while on the board. According to Wikipedia, that started in the mid-1990s. However, you usually needed physical access and/or special software tools to do an overwrite—you couldn't mount these as a filesystem.
UEFI is quite different from legacy BIOSen and can be mounted as a filesystem, but how much it can be tampered with varies between implementations and devices.
So you would have been correct up until about 30 years ago, but not for modern systems.
They should still be possible. It’s not clearing the BIOS though, it is clearing variables loaded into the BIOS. The OS needs to be able to write to them. A good one limits what an OS can write or rebuilds them, a bad one bricks.