The computer in the TV is not running Windows, Apple, Linux or such so none of these downloads would run since the TV is not using a standard OS.
The APK would be for Android which again I've yet to see Samsung deploy an Android TV. They have Tizen but that's not Android.
It sounds like you want an Android or Windows machine in the TV but Sony tried that years ago and the buyers didn't buy and it went away.
There are Android and other boxes we can use to make our TV as smart as we wish.
I have a Samsung UE40J5200AW and Have used it for 1 month. I have found that the Smart Hub only allows the pre-installed TV streaming and movie apps to work. Downloads of other free streaming apps are blocked. In fact it is stated in the browser specifications that all downloads are blocked irrespective of their purpose. I spent a considerable sum on this set, all smart TV´s I know about will allow you to download your choice of apps but not this one. Is this a new Samsung policy to block all but their choice of apps?
The main point of this post is to find a way to un-block the browser so I can download MY CHOICE of apps such as Show Box. I tried downloading the Showbox.APK to a pen drive but the TV is programmed to ignore all app installation files! Possibly there is a way of allowing installation via pen drive instead of the browser, either way would suffice. They do not show up on screen even if you select "All" files. I hope there is a solution to this problem, I am sure I am not the only person with this issue