It’s less of a joke and more of a “huh, isn’t it curious this is possible”
Jokes are usually funny.
The joke is that who would ever actually use their monitor in a diagonal orientation? It's funny that someone actually did it, that's all.
Humor is usually subjective.
I have to disagree on this one. Most jokes that I have heard or read weren't funny at all. And seeing that I'm a dad, most jokes that I tell aren't funny either.