@carlthome I actually came across your solution in a another non directly related thread.
This option is intended to be used both with channels and flakes but it looks like it has some “bugs” in the form of a flake command having channel flags.
When I define it to work with a flake
{ config, ... }:
{
system.autoUpgrade.enable = true;
system.autoUpgrade.dates = "Fri *-*-1..7,15..21 01:00:00";
system.autoUpgrade.flake = "github:${config.userDefinedGlobalVariables.githubFlakeRepositoryName}#${config.userDefinedGlobalVariables.hostTag}";
system.autoUpgrade.randomizedDelaySec = "5m";
}
looking at the file that systemd will execute I can see a single line
nix/store/as1snmyxhr9633n30pbcy2fcbbggii4p-nixos-rebuild/bin/nixos-rebuild switch --flake github:p3t33/nixos_flake#homelab --upgrade
The --upgrade have nothing to do with a flake(and is used with channels) which is updated to the best of my knowledge with
nix flake update