MacRumors published a story that Apple has released iOS 14.0.1 with fix for a bug that resets default apps after rebooting.

Apple Releases iOS 14.0.1 With Fix for Bug That Resets Default Apps After Rebooting

Apple today released iOS 14.0.1, the first update to the iOS 14 operating system that was released on September 16. Today's update is a bug fix update addressing issues that weren't able to be fixed in the initial iOS 14 launch.

Apple Releases iOS 14.0.1 With Fix for Bug That Resets Default Apps After Rebooting