As far as I know there is no official immutable Fedora that uses LXDE - it’s either KDE or Gnome.
You can’t simply install LXDE on a Fedora Silverblue, but have a look at Kinoite, a KDE (and now XFCE) version of Fedora Silverblue. There seems to be a community maintained XFCE variant.
CoreOS is not an alternative to the Workstation product. CoreOS is a minimal cloud or server system made for container-based applications, say for clustered server applications or appliances. Running a desktop in containers seems to be inefficient and a lot of work: Imagine for every app on your desktop you would need a containers…and then they are isolated from each other, nothing you would want on a desktop.
2GB of RAM is nearly nothing these days, but try Xfce or LXDE from https://spins.fedoraproject.org/