The problem with gaming mode is how quickly it falls appart the moment you try to use it for something other than gaming. Something as simple as having more than one window is impossible under Gamescope. That’s pretty problematic when a toolkit decides to implement something as a stealth window, like GTK context menus.

So much text and yet you didn't read that I was explicitly writing about Kirigami apps.

I also think rather than repurposing Plasma Mobile applications like Angelfish it would be better to design new ones that are truly designed for gamepads. Perhaps Plasma Big Picture could be used as a starting point.

Steam Deck has a touch screen. At no point was I taking about docked use.