If you haven’t yet updated your iPhone or iPad to iOS/iPadOS 14 or later, see How to Update your iPhone first. Some browsers and email apps cannot be set as default apps. This is just because the developers of those apps haven’t updated the app with this feature. Some popular apps that can be set as default for email are Spark, Outlook, and Gmail. Popular replacement browsers are Chrome and Firefox.
If you don’t see this option, the app cannot be chosen as the default. Since the feature is new, you may just have to wait a bit for the app to update.
