Help with DE and APP(s) as a NEWBIE

I am a newbie to NixOS

I want to have 2 desktop environments, deepin and gnome(if possible the flashback type gnome version present in ubuntu 18.04) and use the GDM display manager for both.
I want gnome default apps in gnome only other than some of it like nautilus.
and deepin apps only in deepin.
and some apps from different distro’s/de’s across entire nixOS

I would also like to install zram, XDG portal and homemanager and setup everything.
This would also give me a base Idea about managing packages in NixOS, so any help would be appreciated .Thanks in advance.

bump just in case, and I tried googling but did not get exactly what wanted

You should be able to enable gdm as the display manager and both deepin and dnome as desktopmanagers, I don’t think either conflicts with the other and both will show up as desktop entries in gdm. I’m not sure how to isolate apps within each though. All the .desktop files will end up in your nix profile and gnome and deepin will show all of them in their respective menus.

I want to use a different version of app in deepin, for my use.But my mother is instructed to use a old version of some apps.Thats where this comes as a problem.