Do they require it though? I've used a few, but it's always been a convenience thing to use the NFC-scanning app; the alternative is just typing in the details manually.

Kazakhstan has an app (QazETA) for its electronic travel authorization, which is required for many passport holders who want to enter under the visa-free regime. (Perhaps it is not strictly required as one could apply for a visa instead.)

Somewhat confusingly, the iOS App Store description [0] of the app says that it is not a government app, while the rest of the internet and Kazakh government sites say that it is the official government app for the purpose of applying for the ETA.

[0]: https://apps.apple.com/app/id6748705452

Yes. It offers cryptographic proof that you physically have the passport with you. It also gets a digital copy of the photo and other biometrics held on the NFC chip. From a user point of view it reduces the number of typos entered.