I got lots of comments asking questions like whether the TV is smart, whether the TV is used as a monitor with a CPU, is there any dongle connected to the TV, whether it requires internet etc. To clarify all these questions, it is a basic LED TV with Wi-FI and Miracst enabled. No internet, no dongle connected and it is not a smart TV.
The most important question I am trying to clarify here is why some mobile phones do not have mirroring options.
First, you need to understand that screen mirroring works on Wi-Fi network. That means there will be Wi-Fi network setup between your mobile phone and your TV. There is no intermediate Wi-Fi router. There will be an active connection between your phone and the TV. This will not allow you to connect to any other Wi-Fi network for internet. You have to completely rely on your carrier provided mobile data. It may incur a lot of data usage. So, some mobile manufacturers disabled this option from the design itself. This is the case with single band Wi-Fi enabled mobiles.
But the newer mobile phones from different manufacturers supports dual-band Wi-Fi. That means simultaneously you can connect to the TV and to another WI-Fi network for internet. You do not have to rely on your mobile data. Most of the MI Redmi phone supports the dual-band Wi-Fi and they support screen mirroring out of the box.
The solution for those who do not have screen mirroring option is to use apps or third part mirroring devices like Google Chrome cast, Miracast or even Amazon stick. You can also use specific MHL cables which are similar to HDMI cable. Each app may work differently and some apps may require root mobile phones.