The Citadel appears to be
DRM free, but there were some complications in the test. [sorry in advance for the long post]
First, the game requires a newer version o DX11, which the computer I use for testing doesn't have. And since that computer is pretty much always offline, I couldn't update the drivers.
Second, it required some dll files, but even if I placed them in the exe's folder, the missing update for DX11 made it impossible to check if placing the dll files there worked at all.
Because of that, I had to test the game in the computer that has
In the computer with Steam installed, if the game is run directly from the exe with Steam open in the background, Steam doesn't recognize the game as being played (with the game open in the background, I checked in the launcher and in my profile, and in neither it was shown that I was playing the game)
To make sure, I also closed every possible process from Steam, renamed all exes from Steam and then tried to run the game again, and it opened normally.
Tested on Windows 10, but since Steam had already been installed in that computer, I don't know how much it tempered with the test.
Lastly, if someone wants to test the game as well, a word of advice: when you first open the game, hit f11 or alt+enter, go to Preferences > Graphic options and check if the selected resolution is higher than your PC's native resolution (either x, y or both). If it is, change it to any resolution lower than your PC's resolution. If you don't do it, chances are high neither the start screen menus or pause menus will work.