Yes and no, UEFI will look at those vars when determining how to boot the computer but clearing them shouldn't brick the computer.
Basically the UEFI spec is crap to begin with and there are implementations that make egregious mistakes that don't matter if the guest OS is Windows but goes horribly sideways if something atypical comes up.
For instance, a while back there was a case of Linux bricking a bunch of laptops because while efivars had space available, trying to use some of this "free" space would leave you with a paper weight.
Basically the UEFI spec is crap to begin with and there are implementations that make egregious mistakes that don't matter if the guest OS is Windows but goes horribly sideways if something atypical comes up.
For instance, a while back there was a case of Linux bricking a bunch of laptops because while efivars had space available, trying to use some of this "free" space would leave you with a paper weight.
https://mjg59.dreamwidth.org/22855.html