I have a specific custom device that has a Fire OS vNext 7.0 (probably some kind of Fire TV type of the OS?) in it and I need to install my own APK into it.
I have an ADB access with root, but Developer Options are not enabled (I cannot access them), so I can't install the APK (adb install throws INSTALL_FAILURE_USER_RESTRICTED). I need to enable Developer Options to be able to enable installation of third party (unknown source) APKs.
I tried to tap the serial number 7 times in Settings - Device and Software - About as mentioned here, but it didn't do anything. I also tried to follow these steps, but the package com.android.settings does not have the shared_prefs directory that is mentioned there (and I didn't find any other settings package that would have such XML). I also tried to push the APK into the device, go to ADB shell (as root) and install via pm (ended up with the same result as adb install)
Is there any way how to either enable Developer Options so that they appear in the Settings menu, or how to directly enable unknown app installation? Or is there any other way how to install my APK?
I know it may sound weird that I have root ADB access without the Developer Options enabled, but that's just how it is, I already got this device in this state.