Revert "Drop iOS 14 and macOS 11 support"

This reverts commit dcef7f47ff.

Shared/Videos/ThumbnailView.swift

@@ -48,19 +48,23 @@ struct ThumbnailView: View {
     }
 
     @ViewBuilder var asyncImageIfAvailable: some View {
-        CachedAsyncImage(url: url, urlCache: BaseCacheModel.imageCache, transaction: Transaction(animation: .default)) { phase in
-            switch phase {
-            case let .success(image):
-                image
-                    .resizable()
-            case .failure:
-                placeholder.onAppear {
-                    guard let url else { return }
-                    thumbnails.insertUnloadable(url)
+        if #available(iOS 15, macOS 12, *) {
+            CachedAsyncImage(url: url, urlCache: BaseCacheModel.imageCache) { phase in
+                switch phase {
+                case let .success(image):
+                    image
+                        .resizable()
+                case .failure:
+                    placeholder.onAppear {
+                        guard let url else { return }
+                        thumbnails.insertUnloadable(url)
+                    }
+                default:
+                    placeholder
                 }
-            default:
-                placeholder
             }
+        } else {
+            webImage
         }
     }