IEM is easier to type than "in-ear headphones" and has become the defacto generic term for them, just like "monitor" has become to mean any stand mount/bookshelf speaker.

Anyway, over the past few years the market has flooded with cheap and very good "IEM-s" by manufacturers like Moondrop, Truthear and others. 30€ can get you a pair that follows Harman curve quite closely and has low enough distortion to allow EQ. Generally they use 10mm dynamic drivers instead of balanced armatures, but they also have more expensive multi-way BA and DD/BA options.

In short, high quality IEM style headphones have become a commodity and you don't need to be an audiophile or muso who's willing to pay hundreds for Shure SE535-s.