Guys!
Finally I Was Able To Successfully Sideload The Apps In Jio Fiber STB,
It Works Fantastically!
There Are Some Complicated Things In Installing Apps, I'll Explain One By One!
You Need Brand New Jio STB (Which Should Have Not Connected To Internet Previously)
Keep Some Apps Readily In USB
ES File Explorer Or Some Other File Managers / Explorer And Some Good Browser With VPN
Let's Begin The Process
Switch On The STB Don't Connect The LAN Cable Or WiFi, Once Booted Plug USB Drive,
Go To Setting ---> Apps ---> System Apps ---> Package Installer Open It, Browse Apk Stored In USB And Install Them,
Once Installed Go To Setting ---> Security Give Them Permission Of Install From Unknown Sources, You Are Done Now Connect The Internet Android Will Get Updated But Your Apps Will Remain In STB,
Later You Can Install Apps From USB & Browser,
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The Most Critical Thing Will Be,,,
First Thing: How Will You Convince Jio Technician To Allow You To Install Apps Before First Use!
Here Honestly I Made Sure Engineer Have Some Weak Technical Knowledge About This Box And Speak Something Beyond His Knowledge About Box Then You Can Install The Apps As Per Process,,,,,