Create an electrical switch and control it over a phone with components that can be salvaged from old electronics.
The app :
https://apkpure.com/remote-controlled-flashlight/sonap.remoteflashlight
, https://i.ytimg.com/vi/h9OU8tE2nOI/hqdefault.jpg
source
2021-05-24
Amazing
"Without a microcontroller", you only need two quad-core phones processors :S