Setting up VM images with nixos is incredibly powerful when coupled with declarative nature of nix language itself.

I am using it for running homelab type services and lab type setups. Here is how I have it working for me:

Create the VM

This is a snippet from a shell script I use

name=nixos1
img=nixos/24.05
cpu=4
mem=8
disk=100
incus launch images:$img $name \
    --vm \
    -c limits.cpu=4 \
    -c limits.memory=${mem}GiB \
    -c security.secureboot=false \
    --device root,size=${disk}GiB

Configure the VM

Assuming you have some nixos configuration, you can upload the config and update the VM.