diff --git a/Yattee/Core/Settings/SettingsKey.swift b/Yattee/Core/Settings/SettingsKey.swift
index 5d7dfe8a..60d1dfed 100644
--- a/Yattee/Core/Settings/SettingsKey.swift
+++ b/Yattee/Core/Settings/SettingsKey.swift
@@ -116,9 +116,26 @@ enum SettingsKey: String, CaseIterable {
     case onboardingCompleted
 
     /// Whether this key should have platform-specific prefixes.
+    /// Platform-specific keys are stored under a `iOS.` / `macOS.` / `tvOS.` prefix
+    /// in both UserDefaults and iCloud, so each platform family syncs independently.
     var isPlatformSpecific: Bool {
         switch self {
-        case .preferredQuality, .cellularQuality, .macPlayerMode, .listStyle:
+        case .preferredQuality, .cellularQuality, .macPlayerMode, .listStyle,
+             // Home layout — different UI paradigms per platform
+             .homeShortcutOrder, .homeShortcutVisibility, .homeShortcutLayout,
+             .homeSectionOrder, .homeSectionVisibility, .homeSectionItemsLimit,
+             // Tab bar (compact size class) layout
+             .tabBarItemOrder, .tabBarItemVisibility, .tabBarStartupTab,
+             // Sidebar layout/selection
+             .sidebarMainItemOrder, .sidebarMainItemVisibility, .sidebarStartupTab,
+             .sidebarSourcesEnabled, .sidebarSourceSort, .sidebarSourcesLimitEnabled, .sidebarMaxSources,
+             .sidebarChannelsEnabled, .sidebarMaxChannels, .sidebarChannelSort, .sidebarChannelsLimitEnabled,
+             .sidebarPlaylistsEnabled, .sidebarMaxPlaylists, .sidebarPlaylistSort, .sidebarPlaylistsLimitEnabled,
+             // Player details panel — iOS/iPadOS only, different on other platforms
+             .floatingDetailsPanelSide, .floatingDetailsPanelWidth,
+             .landscapeDetailsPanelVisible, .landscapeDetailsPanelPinned,
+             // Video swipe actions — touch-gesture feature
+             .videoSwipeActionOrder, .videoSwipeActionVisibility:
             return true
         default:
             return false
diff --git a/Yattee/Core/Settings/SettingsManager+Migration.swift b/Yattee/Core/Settings/SettingsManager+Migration.swift
new file mode 100644
index 00000000..4a0d8bd5
--- /dev/null
+++ b/Yattee/Core/Settings/SettingsManager+Migration.swift
@@ -0,0 +1,74 @@
+//
+//  SettingsManager+Migration.swift
+//  Yattee
+//
+//  One-shot migrations that move legacy unprefixed values under
+//  platform-specific keys when `SettingsKey.isPlatformSpecific` flips to true.
+//
+
+import Foundation
+
+extension SettingsManager {
+    private static let migrationFlagKey = "didMigratePlatformSpecificLayoutKeys_v1"
+
+    // Mirrors `SettingsManager+CloudSync.protectedVisibilityKeys`. Kept in sync manually
+    // because that collection is fileprivate; the set is small and rarely changes.
+    private static let protectedKeysForMigration: Set<SettingsKey> = [
+        .homeShortcutVisibility,
+        .homeSectionVisibility,
+        .homeShortcutOrder,
+        .homeSectionOrder
+    ]
+
+    /// Copies any legacy unprefixed values for keys that became platform-specific into their
+    /// new `iOS.` / `macOS.` / `tvOS.` slots, both locally and (if iCloud sync is on) in iCloud.
+    /// Leaves the legacy unprefixed keys in place so older builds on other devices still work.
+    func migrateLayoutKeysToPlatformPrefixed() {
+        guard !localDefaults.bool(forKey: Self.migrationFlagKey) else { return }
+
+        let keysNeedingMigration = SettingsKey.allCases.filter { $0.isPlatformSpecific }
+        let pushToCloud = iCloudSyncEnabled && syncSettings
+
+        for key in keysNeedingMigration {
+            let pKey = platformKey(key)
+            let legacyKey = key.rawValue
+
+            // Skip if the prefixed form already exists or if the legacy key is the same as the prefixed
+            // key (e.g. on a platform where `platformKey` didn't rewrite it, though that shouldn't happen
+            // for isPlatformSpecific keys).
+            guard pKey != legacyKey,
+                  localDefaults.object(forKey: pKey) == nil,
+                  let legacyValue = localDefaults.object(forKey: legacyKey)
+            else { continue }
+
+            localDefaults.set(legacyValue, forKey: pKey)
+
+            if Self.protectedKeysForMigration.contains(key) {
+                let legacyTimestampKey = "\(legacyKey)_modifiedAt"
+                let newTimestampKey = modifiedAtKey(for: key)
+                let legacyTimestamp = localDefaults.double(forKey: legacyTimestampKey)
+                if legacyTimestamp > 0, localDefaults.double(forKey: newTimestampKey) == 0 {
+                    localDefaults.set(legacyTimestamp, forKey: newTimestampKey)
+                }
+            }
+
+            if pushToCloud {
+                ubiquitousStore.set(legacyValue, forKey: pKey)
+                if Self.protectedKeysForMigration.contains(key) {
+                    let newTimestampKey = modifiedAtKey(for: key)
+                    let timestamp = localDefaults.double(forKey: newTimestampKey)
+                    if timestamp > 0 {
+                        ubiquitousStore.set(timestamp, forKey: newTimestampKey)
+                    }
+                }
+            }
+        }
+
+        if pushToCloud {
+            ubiquitousStore.synchronize()
+        }
+
+        localDefaults.set(true, forKey: Self.migrationFlagKey)
+        LoggingService.shared.logCloudKit("Migrated legacy layout keys to platform-prefixed storage")
+    }
+}
diff --git a/Yattee/Core/SettingsManager.swift b/Yattee/Core/SettingsManager.swift
index 941926da..f625fe59 100644
--- a/Yattee/Core/SettingsManager.swift
+++ b/Yattee/Core/SettingsManager.swift
@@ -252,6 +252,12 @@ final class SettingsManager {
             }
         }
 
+        // One-shot migration: move legacy unprefixed values for keys that became
+        // platform-specific into their new iOS./macOS./tvOS. slots. Must run before
+        // the initial iCloud refresh so it can seed the prefixed iCloud slot from the
+        // current local value before any remote data is read.
+        migrateLayoutKeysToPlatformPrefixed()
+
         // Initial sync from iCloud to local storage (async to avoid blocking app launch)
         // This ensures local defaults have the latest iCloud values before any reads.
         // While sync is pending, suppress iCloud writes from set() to prevent stale