> I recall reading a news article from a few years ago that said that the Japanese citizenship test is almost impossible to the point that few people try.

Did they substantiate this claim at all? All available public information is that the vast majority of those who try succeed.

People largely don't apply for citizenship, in part because Japan requires them to renounce other citizenships to do so, and in part because a permanent resident can do almost anything that a citizen can in practice.