Can't rebuild system

[waffle8946]

Failed to install bootloader warning: error(s) occurred while switching to the new configuration

I was not intending to be that haphazard. In /boot/EFI/nixos/ you will see kernels and initrds. I manually delete the older versions in that directory, then delete some old NixOS generations + gc using sudo nix-collect-garbage --delete-older-than <whatever>, then sudo nixos-rebuild boot.