On start up the Itch app does not prevent the Mac from going to sleep. However once I run anything from the Itch app, the app then prevents the Mac from sleeping. I am running Sequoia 15.6.1 (24G90) on a Mac Mini M4.
Not an Apple bug. Individual apps can request that the OS not sleep while they're performing a specific task. Usually this is a game running in full screen, or an app that plays video. Somehow the Itch app is incorrectly setting that flag after a game is run.