There's a crossed out padlock button on the right that toggles something, presumably encryption. It's the same icon in both states, only the color changes from red to blue, together with the recipient's text color. In the "red" state, there's also an opened padlock icon next to the recipient's name.
I thought, maybe they assumed sighted and non cognitively impaired users could infer what that's supposed to mean (I could not with enough certainty), so I went to check what VoiceOver says, and... that button literally says, "Button". Nothing else. 🥴
