On normal Linux distributions, there is not much work to be done after installing Steam. Just launch it, wait for it to download the newest runtime, login, install Proton, then start playing the games/apps you just installed. Currently on an LFS system with current GLFS packages and configuration, getting games and apps to work takes one more step, one that must be repeated for every game and app you install.
Any game or app, native or not, will fail to launch for an unknown reason. It will attempt to launch, and by the time a window should be created, Steam will fail and shut down the process. This can be resolved by going into the game or app's launch options and set the following:
LD_PRELOAD="" %command%
The game or app should now proceed to launch just fine. Work is
being done here and there to find out why it is necessary for every
game or app, but it might be failing to find libraries in
/run/host, despite libraries being
located in /lib, and if you're on
x86_64 and did multilib, /lib32.
If the steam overlay is desired, enter the following launch option instead:
LD_PRELOAD="$HOME/.local/share/Steam/ubuntu12_64/gameoverlayrenderer.so" %command%
This launch option loads a library necessary for the steam overlay to function.