Modifying / Setting / revoking permissions of Android application (system? )via adb, android 11 (miui 12.5 eu)

Question

I'm a Basic Newbie trying to make changes on my phone ;-) maybe you can help me.

I'm trying to limit the amount of data I share with Xiaomi & google while using a xiaomi phone.

Since the unfortunate update to miui 12.5 I cannot define the permissions I want using Setting=> Apps=> Manage apps => permissions.

For example:

Miui Bluetooth ¦ location permission : preselected "Allow only while using the app". I cannot change this! All options are grey!

I also have an issue when I try to limit the data access. Specially the background data, and WIFI.

I am hoping to be able to make some changes over adb, but I've no idea how... just managed to see the permissions for each app.

The phone is not rooted, and the stupid xiaomi unlock... doesn't work (your device is not recognized when I connect it over USB).

Thanks for your help! (please explain things as if you'd try to explain it to your Granma :-))