If your MBTI is fixed because it is based on how you answer questions so long as it is without the intent to alter its outcome, then it is not anymore deterministic than a horoscope.
I fail to follow your logic here. The idea is that the answers you give - which are assumed here to be “without the intent to alter” - are based on your personality, and can therefore be used to measure it. I’m not sure what the word “deterministic” means in this context, but the answer do not determine the personality - they are determined by it.
“Fixed” is also not a good word - one’s personality, and the way they answer such questions, can change during their lifetime as they get older and shaped by experiences.




The bees are your friends.
As long as they are still around, that is…