The flu absolutely kills healthy, young individuals.
I personally know an otherwise healthy 18 year old who died of the flu.
Edit: mine is a completely factual statement. I’m not sure what the issue is, but a later comment is making me think I should tell people to Google “long flu”.
Some viruses are not so bad. Both COVID and the flu are bad. Hopefully, we can control this with something like a combined flu/COVID annual shot (and maybe we should start calling it that instead of a booster). Both are not the same as, e.g., smallpox where it’s kinda “one and done”.