Graphics > "External display" on iOS and Android. "Show the game" (the
default) is the TV mode, "Mirror the screen" leaves the TV to the system.
A change applies right away. It's disabled on backends that can't draw to
a second swapchain.
On Android 12 and up, a second screen that's part of the device (like a
dual-screen handheld's) isn't used, so the game doesn't move there by
itself.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>