Fossery Tech 
I installed Debian 12 without GUI on a VM, then installed IceWM and LightDM on it, but I couldn't get LightDM to start IceWM. I tried hard for 5-6 days then ended up reinstalling Debian with default GNOME and using IceWM with GDM 😂
There are things that just don't worth the hassle
Update: I finally got IceWM working with LXDM, thanks to this video:
https://redirect.invidious.io/watch?v=AxaZpIB35Vs
❄️ freezr ❄️@fosserytech it won't work if you don't create a Xsession file: https://wiki.debian.org/Xsession
Right now you're loading the full GNOME backend to run IceWM...