@mjgardner not really, no. Feditext uses Swift structured concurrency and more SwiftUI than Metatext before it, but so far, iOS 15 and macOS 12 still have all the features we need, or close equivalents.
it helps that we don't pull in a lot of 3rd-party code, and what we do use is extremely broadly available: Feditext's major 3rd-party dependencies are SDWebImage (iOS 9+, iOS 13+ for SwiftUI) and GRDB (iOS 11+).