Extremely unfun fact: before even the Jews, they came for LGBTQ+ people. The first major Nazi book burning was at the Institute For Sexuality which, apart from being a research institute dealing with all sorts of "nonstandard" sexuality in a scholarly rather than punitive manner, was also the world's first trans clinic.

The reason it's not mentioned is that Pastor Niemöller, being a conservative pastor, didn't see anything wrong with the persecution and erasure of LGBTQ+ people.

One of the reasons it's important to remember that the LGBTQ+ community were the first targets of concerted Nazi erasure even though they were far from the first targets of nazi hatred and slander is that the GOP are doing the same thing and they'll go through the rest of the list too if they aren't stopped.