[Android Q&A, Help & Troubleshooting] lforlalit:
I made some critical progress on this. Go to this path Storage 1 > etc > sysconfig. There's a file named hiddenapi-package-whitelist.xml. I am pasting the content below.

<?xml version="1.0" encoding="utf-8"?>
<!--
- Copyright (C) 2018 The Android Open Source Project
-
⁃Licensed under the Apache License, Version 2.0 (the "License");
⁃you may not use this file except in compliance with the License.
~ You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
⁃Unless required by applicable law or agreed to in writing, software
⁃distributed under the License is distributed on an "AS IS" BASIS,
⁃WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
⁃See the License for the specific language governing permissions and
⁃limitations under the License
-->
<!--
This XML file declares which system apps should be exempted from the hidden API blacklisting, i.e. which apps should be allowed to access the entire private API.
Only apps NOT signed with the platform cert need to be included, as apps signed with the platform cert are exempted by default.
Do not include any apps that are updatable via Play store!
-->
<config>
<hidden-api-whitelisted-app package="android. ext.services" />
<hidden-api-whitelisted-app package="com.android.apps.tag" />
<hidden-api-whitelisted-app package="com.android basicsmsreceiver" />
<hidden-api-whitelisted-app package="com.android.bookmarkprovider" />
<hidden-api-whitelisted-app package="com.android.calllogbackup" />
<hidden-api-whitelisted-app package="com.android.camera"/>
<hidden-api-whitelisted-app package="com.android.bookmarkprovider" />
<hidden-api-whitelisted-app package="com.android.calllogbackup" />
<hidden-api-whitelisted-app package="com.android.camera" />
<hidden-api-whitelisted-app package="com.android.car.dialer" />
<hidden-api-whitelisted-app package="com.android.car.messenger" />
<hidden-api-whitelisted-app package="com.android.car.overview" />
<hidden-api-whitelisted-app package="com.android.car.stream" />
<hidden-api-whitelisted-app package="com.android.companiondevicemanager" />
<hidden-api-whitelisted-app package="com.android.dreams.basic" />
<hidden-api-whitelisted-app package="com.android.gallery" />
<hidden-api-whitelisted-app package="com.android.launcher3" />
<hidden-api-whitelisted-app package="com.android.mtp" />
<hidden-api-whitelisted-app package="com.android.musicfx" />
<hidden-api-whitelisted-app package="com.android.permissioncontroller" />
<hidden-api-whitelisted-app package="com.android.printservice.recommendation" />
<hidden-api-whitelisted-app package="com.android.printspooler" />
<hidden-api-whitelisted-app package="com.android.providers.blockednumber" />
<hidden-api-whitelisted-app package="com.android.providers.calendar" />
<hidden-api-whitelisted-app package="com.android.providers.contacts" />
<hidden-api-whitelisted-app package="com.android.providers.downloads" />
<hidden-api-whitelisted-app package="com.android.providers.downloads.ui" />
<hidden-api-whitelisted-app package="com.android.providers.media" />
<hidden-api-whitelisted-app package="com.android.providers.tv" />
<hidden-api-whitelisted-app package="com.android.providers.userdictionary" />
<hidden-api-whitelisted-app package="com.android.smspush" />
<hidden-api-whitelisted-app package="com.android.spare_parts" />
<hidden-api-whitelisted-app package="com.android statementservice" />
<hidden-api-whitelisted-app package="com.android.storagemanager" />
<hidden-api-whitelisted-app package="com.android.systemui.plugins" />
<hidden-api-whitelisted-app package="com.android.terminal" />
<hidden-api-whitelisted-app package="com.android.wallpaper" />
<hidden-api-whitelisted-app package="jp.co.oronsoft.openwnn" />

<!-- TODO: Remove NetworkStack whitelisting -->
<hidden-api-whitelisted-app package="com. android. networkstack" />
</config>

you see these are the system apps that can be accessed directly. my workaround is to just add these two lines in this code.

<hidden-api-whitelisted-app package="com.android.settings" />
<hidden-api-whitelisted-app package="com.google.android.packageinstaller" />

This should enable the Android Settings app and Package Installer app in the System Apps section.

BUT... i am not able to edit the file or replace the file using the default explorer. If anybody can suggest any way to replace or edit this file, we can actually have very high chances of sideloading all the apps we want on jio airfiber STB.

Anyone has any ideas on this?