If either the TV or the remote is too new or too old,
they may not work together.
Manufacturers change remote command sets from time to time,
usually when new features are added,
or when the overall design of their products is significantly altered.
It can also happen if they don't actually design any of their own stuff from scratch
and rely on outside sources. If the source changes, the remote commands will, too.
The remedy here would be trying an older universal remote,
or, preferably, getting an "original" remote.