Programs may read from /etc, but it’s not recommended. Instead, I recommend having your .config directory stored somewhere, or preferably, have all configs in a git repository (often called dotfiles) and deploy them on systems for example with stow

System wide configuration files

Also, if you are using xorg-xinit, make sure that you copy everything from /etc/X11/xinit/xinitrc into your ~/.xinitrc (and replace everything from twm & with your own stuff). If you don’t to this, systemd will not get $DISPLAY, leading to xdg-desktop-portals failing to work, also causing long startup times.