I must admit when my father in law, who had dementia, was living with us we always let him watch Coronation Street (as this is what he had always done) while we found something else to do as we were not into the soaps.
One night when we heard a lot of shouting on the TV we asked him what was going on and what they were all arguing about and his reply was he didn’t know. In fact when asked he didn’t know who was who or what the programme was. He could no longer follow a story or differentiate what was real and what was not as he thought some of it was down the road when they showed country lanes.
This was the day we turned it off and got him a set of wireless earphones so we could play him music he liked. https://www.spotify.com/uk/ is great for this as it has every type of music you can think of. He was then a happier man.
It would be good if there was a specific channel on the TV with nice happy programmes that are suitable for those with dementia so that you don’t have to worry about what they are watching that could alter their state of mind and behaviour.