@trevdev weird it works flawless on my systems. Here is my config if you are still interested to tinker with:
services.greetd = {
enable = true;
useTextGreeter = true;
settings = {
default_session = {
command = "${lib.getExe pkgs.tuigreet} --time --remember --remember-session --cmd niri-session";
user = "greeter";
};
};
};

And yes user is just "greeter" when I used my user name it broke