To play Duck Hunt with touch Lightgun on Switch, you have to use the Fceumm core, and ENABLE the touch lightgun in quickmenu-option.
Step By Step instruction:
- Install the latest nightly from here:
http://buildbot.libretro.com/nightly/nintendo/switch/libnx/
(Or at least go to online updater and update your Fceumm NES core.)
- Start Retroarch
- Load Content
- Select Duck Hunt
- Select the "fceumm" core.
- Start a Duckhunt game
- Go to menu
- Select Quickmenu->Options->Touch Lightgun->Enable (or something similar)
- Play Duckhunt with Touch
Other Touch input works too.
For example, you can use touch to control the Paddle in Arkanoid on Mame. Just go to quicmenu->options and set "Mouse Control->Mouse".
Or, you can use touch to control the mouse pointer in DOSBox games.
Or, you can enable the controls overlay and push the virtual gamepad buttons on the screen with touch, like on a smartphone. But there's really no reason to do that because the Switch has Joycon controls.