Is this really true? I’m sorry, but I don’t believe it even for a minute.
The only scenario when this is remotely true would be if you applied a BIOS update to an out of warranty piece of hardware, which then died. Obviously, in this case you would have no warranty left and thus no support, but in the case of OP this is a new machine.
Would be interested in a link to any custom builder or major OEM that says that BIOS updates would invalidate their warranty…