I don't think using a bootloader password is a very common way of (attempting to) secure a computer. At least I have never used it nor thought it could actually

I don't think using a bootloader password is a very common way of (attempting to) secure a computer. At least I have never used it nor thought it could actually secure my computer (at least without locking out the bios/uefi to allow booting from other media and enabling secure boot). So on any of my PCs, you could just press F10 to get access to the grub rescue shell. I think that bios/uefi passwords and disk encryption are much more commonly used to prevent unauthorized access to an intruder with physical access to the computer when it boots.