Since this thread is the number one result on google for how make nixos boot usb
Here is the normal people answer
Go to Download Nix / NixOS | Nix & NixOS
download either Gnome based installer boot ISO or the KDE based one
https://channels.nixos.org/nixos-23.05/latest-nixos-gnome-x86_64-linux.iso
https://channels.nixos.org/nixos-23.05/latest-nixos-plasma5-x86_64-linux.iso
Go to rufus’ website Rufus - Create bootable USB drives the easy way
download latest rufus https://github.com/pbatard/rufus/releases/download/v4.2/rufus-4.2p.exe
Start rufus
Drag and drop your nixos ISO into rufus
Click device, make SURE you have selected the right device
Hit start
then hit OK
Hit YES
Hit OK to confirm you have the right drive and it will be deleted
You now have a bootable USB nixos installer