I have found a solution.

If I bypass the Slitherine launcher (autorun.exe) and run the game directly (Aggressors.exe) it will start on my primary monitor.

Hi, The game always starts on my secondary monitor if I select fullscreen in settings. I tried setting to windowed mode and move to the correct monitor, then change to fullscreen in settings but it always restarts on the secondary monitor. You have no setting in graphics options for borderless windo...