Remote controls handsets, often become difficult to work after a certain time, this is a very common problem and happens to all sorts of devices that get daily use, TVs, recorders, settop boxes, even garage doors and air conditioners can have this problem.
In most cases it is easily repaired by servicing the remote control, this is necessary due to dust and liquids that can get inside the remote, it is possible to open the remote and inspect it for this sort of problem.
With modern smart TVs some remote handsets require "pairing" this is a process where the handset is matched to the TV. Usually part of the initial setup when first installed, it can become a required adjustment later in the TVs life.
A not paired remote will usually only work on a few functions, like on/off etc smart features and on screen pointer will not be available until pairing has occurred.
I the WIFI receiver inside the TV is faulty, the smart features on the remote may also not work.