No knowledge is useless. Even though some obscure trivia only seems to come in handy at parties or quizzes.
Even listening to somebody talk about a topic you seemingly already master can be interesting. Perhaps a new angle provides a fresh perspective?
The knowledge that seems unimportant at a particular moment in life might be useful somewhere down the road. Maybe someday you can help a friend by sharing some insights on a topic important to them.
As for the chunks of knowledge that you can’t put to good use, knowing what doesn’t interest you helps you (re)define your interests.
No knowledge is useless.