We all have different problems. I cannot install Facebook or Messenger on a Sony phone.
due to a permission, that used to be defined by Sony in pre-Android 7 and now is defined by Facebook, i.e. by app with different signature. The old permission definition still lingers on the phone and the only way to get rid of it is to reset the phone to factory settings. Which I'm obviously not going to do.
What phone are you using? I've had a Galaxy S3, S5, and now S7. I can (and have) uninstalled Facebook on all of them. None of them came with it installed?
due to a permission, that used to be defined by Sony in pre-Android 7 and now is defined by Facebook, i.e. by app with different signature. The old permission definition still lingers on the phone and the only way to get rid of it is to reset the phone to factory settings. Which I'm obviously not going to do.