Not sure if this is a bug or a documentation issue, but all documentation I've found indicates that Piglins spawn on peaceful difficulty... full stop. However, I was all over the Nether Wastes and never found a single Piglin... until I went into the Nether wearing a golden helmet. Then I saw one almost the moment I entered the wastes.

I did open a chest right in front of that Piglin, and he did not despawn, so I'm guessing the issue is more, "they're not spawning," than it is, "they're despawning if they'd otherwise be hostile."

Anyway, even if this is intended behavior, I still wanted to get it noted, since everywhere else on the Internet indicates that there are no caveats to Piglins spawning in peaceful.