While trying to update my display name, I've realized that any display name longer than 20 characters gets rejected (specifically: https://lemmy.ml/api/v3/user/save_user_settings returns 400 with {"error":"invalid_display_name"}). Some digging through the code seems to explain why: Lemmy 0.19.20 (the version running on lemmy.ml) uses the same config option for limiting display name length as it does for usernames, which defaults to 20 (and .ml hasn't changed it from the default value)¹.

I would be satisfied with that explanation, except there are clearly other users on my instance whose display names exceed 20 characters (example: https://lemmy.ml/u/Trying2KnowMyself). So, my question is: how the heck are people able to set these longer display names?

¹ In the 1.0 betas the config option seems to have been replaced with hardcoded limits which are separate for user- and display names, but I don't think that'd be relevant since that's not the code which .ml is actually running

EDIT: I figured it out! Importing user settings from a json backup bypasses display name validation. Most likely the user I referenced as an example had imported their profile from their Hexbear alt, so it ended up just copying their display name over as well.