Anyone can make an MBTI test and call it legit, and they do. There's a truck load of shit out there that's just based on the author's dumbass opinion of the kind of people the types are. There is absolutely a sub-culture that treats MBTI as ScienceZodiac like >>52944579
mentions and it's annoying as fuck. THAT SAID, legitimate tests exist, tests based on the original ideas of MBTI, and I think they're worth finding and doing right. I am entirely unnerved by how spot-on accurate my type was for me, and I've taken a lot of for-fun personality tests in my life. This was the first one that kind of made me step back and put some weight on it.
What really really sold it for me was when I found a few little communities of people with the same type and discovered I had a lot in common with them outside of the test results. Struggles, talents, frustrations, vices; similarities way beyond what I've ever had in common with even the closest friends.
This is the test I took and I recommend it to anyone who's interested: https://www.16personalities.com/free-personality-test
Their methodology and trait labeling is consistent even if their characterization of the types are a little narrow.
As for the OP>>52937516
No, it's much easier to shape personality via backstory than to contrive a backstory from a personality.