I often suspect things in Settings, esp. account/iCloud section to be webviews, just based on how they load (icons appearing a short moment after the page opens for example).

Yes, those parts of the Settings app are built with web views that embed React Web:

https://news.ycombinator.com/item?id=30648424

Oh so that's why they're terrible and often break with no error messaging or recourse

Probably, but it’s not as if the native parts of Settings are much better.

When you tap some of the menu items in the “Saved to iCloud” section, they don’t have the normal grey item highlight that happens with the rest of the settings app.