Xiaomi
Manage App Permissions auf Xiaomi
MIUI only asks for a permission once, right when an app first tries to use a sensor or a set of personal data such as contacts, location or the microphone. Whatever you tap in that first pop-up, Allow or Deny, becomes the fixed state for that app until you change it manually. This is why features can suddenly stop working days after installation: the app itself has not changed, but the one-time answer you gave is still active.
To review or reverse that decision, go to Settings ➔ Apps ➔ Manage apps ➔ choose the app ➔ App permissions ➔ choose the permission you want to check ➔ pick Allow or Deny.
This screen lists every permission the app has ever requested, not just the ones it asked about on first launch. That matters for apps that added new features later, since new permission requests can appear here even if you never saw a pop-up for them.
If an app misbehaves after you grant a permission, a force stop or reinstall clears cached state and is often a faster fix than toggling permissions back and forth. Revoking a permission that an app depends on for core function, such as storage for a file manager, can make the app unusable until you restore it.