After updating my AMD drivers because WoW patch 10.1.5 said they were out of date, my Diablo IV stopped launching. WoW worked fine and the message disappeared. Diablo IV Launched in task manager, ran CPU to 100%, but did not launch into the game on screen. Stumbled across this post, downloaded the April 27, 23.4.2 version of AMD driver and Diablo came back. So kudos to the OP, you fixed the issue. Now I need to check all other Blizzard games for potential issues.