To me, they certainly are.

However, many people seem to think that you can get smarter. There’s even a YT channel with a name like that, so I guess smart means something different.

Fair enough, we can split that nebulous concept into innate intelligence which refers to your mental capacity, and being booksmart, i.e. having read many books and knowing stuff. In that sense, you can get smarter by learning more information or mastering new tools.

Getting more intelligent happens naturally as children age, but eventually it’s all downhill. You can choose to drink alcohol and and reduce your intelligence that way, but I’m not aware of any method of increasing your intelligence. Many people seem to use this term in a very different way, so I might be in the minority here.

Either way, I would still argue that, intelligence isn’t something you can simply increase.