On the other hand, it feels wrong to me to call these "myths" when they are really just simplifications.

(And I have heard of the 80-bit internal register thing described in https://news.ycombinator.com/item?id=44888692 causing real problems for people before. And --ffast-math is basically spooky action at a distance considering how it bleeds into the entire program; see e.g. https://moyix.blogspot.com/2022/09/someones-been-messing-wit....)