For the unaware, you can install Steam as flatpak by first installing flatpak: https://kaosx.us/docs/flatpak/
Then adding the 'flathub' remote:

$ sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

And finally installing Steam:

$ sudo flatpak install flathub com.valvesoftware.Steam

To run it, just:

$ flatpak run com.valvesoftware.Steam