Years ago, aged eighteen, I joined MENSA. I left after a year, having seen ample evidence to support the old description of MENSA as “The society for people impressed by their own intelligence”. In truth, the whole organization was creepy.
Anyway, when I applied they sent me an IQ test which you sent in to be scored. If you scored highly enough they asked you to attend a monitored exam. I scored 158 on the test at home and 159 when I went to London to be tested.
I have never encountered anything, either at school, university or at work that has been intellectually difficult for me.