CH_ASUSI'm not looking for currently supported apps, though. I'm looking for a way to *manually add apps* to that list, similar to how Microsoft has on their Xbox Game Bar for Windows 10 or other Android device manufacturers have for their game modes, and if that feature is currently supported, please make it easier and straightforward.
You may go to Settings->Advanced->Game Genie
Then click the "Game toolbar" text (dont click the toggle click the text area to the left of the toggle, separated by the | )
There you will see all apps that Game Genie can be enabled for .