In time when i use FTNoIR yes, we need to put that .dll in DCS/bin folder but i don`t know what situation is now about that.
But for Opentrack you don`t need that, just install and all work fine.
Just download from this link: https://github.com/opentrack/opentrack/releases
Install, i recommend to you chose Acela filter in settings, ... and other settings is easy to set for you. And run the app.