They can negotiate to make time for private interests (and, of course, they can pick and choose worthy causes to adopt as official duties that coincide with said interests). Their time may be pre-planned, but of course they can get to theatres, movies, concerts or spend an evening with a book if they want.
There’s also a celebrity=instant expert effect.
If Charles opined on his preferred flavour of ice-cream it would be publicized and discussed in a way that my far more nuanced and brilliant random opinions would never be. There is an audience commenting on the opinion, but a much bigger crowd arguing about whether Royals / rock-stars / Kardashians should be allowed to have or express opinions at all [plus the associated ‘What do they have against pudding / cheese platter’ reactionaries].
In Charles’s defence, his opinions on architecture and urban design represent a life-long passion. One of the Royals’ privileges is becoming a patron of societies and movements that they are often genuinely passionate about, and getting the chance to meet experts and keep up with all the current concepts.
Any idea that someone like Charles would not have time to read for leisure is nonsense.
The guy has to sleep, so he might read in bed. He spends a lot of time travelling. I read on the train and I bet he can read on his helicopter. Like the rest of us, I bet he often finds himself waiting around for something to happen.
I don’t know, but I bet that he would rather read a book/listen to music than watch Love Island.