I’ve got a couple games installed from Steam onto an external SSD (Dragon’s Dogma: Dark Arisen is the game in question - listed as supported and it only has one trainer in it’s history), and the app can’t find it. Reinstalling the app, rebooting my PC, made sure my AV wasn’t interfering, etc. did nothing. Set the location manually by finding the game exe, but when I start the game it says “We’re having trouble starting or finding your opened game.”
Thing is the app runs fine on games in my main Steam install directory. Just doesn’t seem to notice my SSD.