Nix / NixOS

I need to use multiple ? in one of my flake input's url, the issue is only the first ? gets registered but not the second. I've tried github:SteamClientHomebrew/Millennium?tag=latest?dir=packages/nix which returns this:

error:
       … while updating the lock file of flake 'git+file:///home/claymorwan/.dotfiles?dir=NixOS'

       … while updating the flake input 'millennium'

       error: path '«github:SteamClientHomebrew/Millennium/fcb0e5627deecf2fc03067ee3dfb63d37e8e82d4»/flake.nix' does not exist

Then I've tried github:SteamClientHomebrew/Millennium?dir=packages/nix?tag=latest which returns this:

error:
       … while updating the lock file of flake 'git+file:///home/claymorwan/.dotfiles?dir=NixOS'

       … while updating the flake input 'millennium'

       error: path '«github:SteamClientHomebrew/Millennium/fcb0e5627deecf2fc03067ee3dfb63d37e8e82d4»/packages/nix?tag=latest/flake.nix' does not exist

I've also tried to write the input differently like this

millenium = {
  type = "github";
  owner = "SteamClientHomebrew";
  repo = "Millennium";
  tag = "latest";
  dir = "packages/nix";
  inputs.nixpkgs.follows = "nixpkgs";
}

which also didn't work and returns this

error:
       … while evaluating flake input
         at /home/claymorwan/.dotfiles/NixOS/flake.nix:48:5:
           47|
           48|     millennium = {
             |     ^
           49|       type = "github";

       error: input attribute 'tag' not supported by scheme 'github'

So not really sure how to set that up