You can get a black belt on the Internet… In less than a week.
I wouldn’t recommend it, though.
Internet technology has improved a lot of things, but fighting isn’t one of them.
In the past, by definition, a black belt meant you were someone to be feared. Then the Ultimate Fighting Championship happened. Now, because of Brazilian Jiu Jitsu, people ask, “What style do you practice?” The value of a black belt in karate was seriously devalued when BJJ disrupted martial arts.
It can take a decade or more to become a black belt in Brazilian Jiu Jitsu. But it’s worth it.
How long have you practiced your skill? What is your personal version of BJJ? As long as there are humans to engage with, you can earn a black belt in something.