I just bought Section 8: Prejudice for $ 2,49 using the SUMMER10 code at https://www.fanatical.com/en/game/section-8-prejudice

Despite what the Fanatical and Steam store pages say, multiplayer still works (and thus also the creation of a profile, allowing you to save progression in singleplayer). But almost nobody is aware of this, causing empty matches.

Step 1: In your control panel uninstall the Games for Windows Live Redistributable that Steam automatically installed when you first launched the game.

Step 2: Go to (...) and click "If you have a Windows 7, Windows 8, or Windows 8.1 device, click here, and then follow the steps to install the Games for Windows Live app." (also if you have Windows 10!). Download and install this newer version of Games for Windows Live, ignore the connection error after installation.
EDIT 2021: Try https://go.microsoft.com/fwlink/?LinkID=201134 or https://community.pcgamingwiki.com/files/file/1012-microsoft-games-for-windows-live/

Step 3: in C:/Program Files (x86)/Steam/steamapps/common/Section 8 Prejudice, right click on S9.exe, click Properties and under the Compability tab, set the Compability mode to Windows 7.

Step 4: start the game, Games for Windows Live will ask you to login to your existing Xbox/Live account and to enter the serial number for the game. Steam will helpfully display the serial number in a popup constantly. Enter this serial number, which will bind the game to your Xbox/Live account.

Step 5: The game will download a Games for Windows Live update. The game will ask you to close the game, do this and the update will install automatically.

Step 6: After the GFWL update has been automatically installed, restart the game, log in again with your XBOX/Live account. It will download your profile, and all the options will be unlocked, like saving progress, unlocks, and multiplayer.

I'm off to play the Conquest gamemode (the game supports bots until players join your match). See you on the battlefield!