Hi there NA120,
I’m happy to see that you posted to the Apple Support Communities for assistance and I understand that you're having issues enabling the flashlight. It’s my pleasure to assist you.
Is your iPhone using the latest version of iOS? At the moment, that would be iOS 13.3.1 The steps here will help you with updating if needed: Update your iPhone, iPad, or iPod touch
Also, try restarting your iPhone: Restart your iPhone
If the issue persists, reach out here for additional support: Contact Apple Support
Take care.