Humankind = all humans, and it’s considered more gender-neutral and modern.
Mankind = also means all humans, but some people feel it sounds male-centered because of the word “man.”
Examples
“Humankind has made huge technological advances.”
“Mankind has explored space for decades.”
Both are usually understood the same way, but in schools, workplaces, and modern writing, “humankind” is often preferred because it includes everyone more clearly.
Here you go H&M - Hakuna Matata 🦁☺️