Open the Terminal application by searching for Terminal after pressing the Super Key , .
Once the Terminal application is opened you can use the Command Line tool
apt to search for it like so:
apt search steam
Once we find the right name for Steam we can install it with
apt as well. Please type this command into the terminal and press Enter:
sudo apt install steam
Be very careful when using sudo with ANY Command. It can make system wide changes so be sure to read everything before entering ‘Y’.
Once installed, use the Activities Overview to search for and run Steam.
Open the Pop!_Shop application then either search for Steam or by clicking the Steam icon on the Pop!_Shop home page.
Then click the install button.
Proton is a way to enable support for some Windows games using Wine and some tweaks and additions that Valve have been working on. You can enable it using the the Steam Settings to download and install Proton.