Does your device refuse to work when you use one of your apps? If that’s the case, delete the app.
Make sure your iPhone is up to date. iOS 14.4.1 has been released just a few hours ago. Maybe that’ll help with your problem.
Force starting your iPhone might help: press and hold Power and Volume Down button until you see the Apple logo. As soon as it appears, let go of both buttons. Your device will power up on it’s own.
If that doesn’t help, backup your iPhone and set it back to factory settings: Restore your iPhone, iPad, or iPod to factory settings , then restore it from the backup,
or put it into DFU mode: How To Put An iPhone In DFU Mode, The Apple Way