In the backend, it's basically regexp, but keeping it simple usually just suffices.

My own file, for example, looks like this (and nothing else):


The Escapist 2 might experiencing some other issue that prevents the overlay from showing up and whatnot. You can validate if Special K initializes itself in the game by looking for a folder that matches the name of the game executable below Documents\My Mods\SpecialK\Profiles\


Edit: As the strings are regexp, some characters have special meaning. For example, those periods (.) I have in my list technically means "any character" at that exact position, so e.g. "quake2.exe" would equally match against a process by the name of "quake2aexe". But since those types of processes are basically impossible in Windows, the actual wildcard-nature of a single dot makes no practical difference in my case, and so I can use it.

This is, by the way, why backslashes are using two slashes, as a single slash \ has different meanings depending on the following character. For example \b would mean the match would have to be made at the beginning of a string -- and so subfolders needs to use \\ as the first \ basically escapes the following slash \, so \\ is interpreted as a single \.

I personally don't use slashes at all in my whitelist config because of it. Just typing the name of the executable of the game is usually what I go for.