Some apps can access your location, contacts, calendar events, reminders, and pictures. To check which apps use these, open the Settings app then select Privacy and look into each option to see which apps are accessing those details.
This function can be turned off for each app if you don’t want them to have this access. Note that this might affect usability in some apps.
Limited Photos access
The Privacy settings for Photos are more nuanced if you have iOS 14. Apps now give you the option to only allow access to Selected Photos when granting permissions.
You can review and change these permissions on an app-by-app basis from Settings > Privacy > Photos.