I am having the same exact issue, I try to launch Kotor II via Vortex and Vortex tells me I need to start Steam, which is already running. I only have one drive, so your solution is not the answer for me. I have checked that Vortex is pointing to the correct Steam directory for Kotor II and the path as well as the executable name are correct. Vortex worked perfectly for me while playing Fallout 4 and both games have been installed in a Games folder on my system (under Steam). Just FYI, I have played this game in the past through Steam just fine and have launched the game through Steam after Vortex displayed it's error message. This is definitely an issue with Vortex correctly identifying that Steam is up and running, which is odd since Fallout 4 didn't have this problem.
