Moreover, if your app does not process any personal data – eg. it is a calculator app without sign-in functionality – you don’t need a privacy policy at all. Keep in mind that the privacy policy may be required by some 3rd parties. For example, at the time of writing, it is required by Google Play Store when targeting users younger than 13 years old. If you only target older users, a privacy policy is optional.
However, starting from April 1, 2022, it becomes mandatory for all the new apps. The privacy policy of the app is always required by Facebook. This is obvious because the personal data needs to be processed in order to sign in to the user.