It's possible to disable third party keyboards for sensitive data entry at least on iOS. Not sure if the same is possible on Android – worst case, a wallet could just provide their own keyboard/passphrase entry method.

> The same way you verify anything is what you want and stays that way, MD5/SHA256 hashes and airgaps.

How do you determine a given hash to be trustworthy? And how do you know you can trust your `sha256sum` implementation?

You're always trusting someone. Any security analysis pretending otherwise is worthless.