How to lunch niri on non NixOS Home Mannager setup?

I have problem to properly start niri seted up with Home Manager on non NixOS os (Arch Linux).

As far as I understand niri-session is the way, but calling it from a tty session results in error about missing niri.service. This can be “solved” by following this, but it looks like not everything is loading correctly as for example firefox is not following the stylix configuration. Stylix works ok when niri is lunched just from niri bin. I’m quite confused.

Do you know what is the best way to lunch the niri desktop session?