Double tap on back inconsistency issue
I enabled Touch double tap to turn on/off my flashlight. Sometimes it works. Sometimes it doesn't. Very inconsistent. However, I think I may have discovered the solution. I think pressing the side button between on/off cycles makes it more consistent. I have no idea why this works, but it seems to help. If you've already made sure Touch is enabled and set to your desired action, and it's still not working, try pressing the side button before double (or triple) tapping. Hopefully, this helps.
iPhone 16 Pro, iOS 18