Anyone found anything in the .Ini files or anywhere to block controller in game?

Just tried the demo & it just has me moving slowly backwards because I've a controller plugged in :/

Yeah, I know, I could unplug it...but devs could at least put in an option to turn controller off or at least to detect mouse priority.

I suppose you are referring to System Shock Enhanced Edition, since it's the only game of the series which uses an ini file. (Please, in future posts be more specific about the game you're referring to!)

Browse to the game's folder and open the sshock.ini file with any text editor.
Look for this line: Change it to: (Note: you obviously have to add the latter, if the former is not already present.)
Save the file and run the game: it shouldn't detect your controller anymore.

The only System Shock on here that has a demo is the new System Shock (demo...), not any of the older versions.

False.

Is that on this site? No.
Is that anything to do with the new one that I've already mentioned? No.

If you're not here to help anyone & content in wasting time, fuck off somewhere else.

Very good-mannered.
I only suggested you to be more clear in your OP, if you want someone to help you. Anyway it's up to you.
And you are right: I wasted my time trying to find a solution for you for the wrong version of the game. Lesson learned, I suppose.

Speaking of the System Shock remake demo, it's not here anymore: it was removed as per developer's request because they changed the game's engine from Unity to Unreal Engine. You can certainly still play it, but the final game will be very different.
I know this is not a solution to your problem, it's just a warning in case you don't know.

Maybe someone else can help you: good luck!