diff --git a/ElementX/Sources/Screens/FilePreviewScreen/InteractiveQuickLook.swift b/ElementX/Sources/Screens/FilePreviewScreen/InteractiveQuickLook.swift
index e416c1c0e..630568987 100644
--- a/ElementX/Sources/Screens/FilePreviewScreen/InteractiveQuickLook.swift
+++ b/ElementX/Sources/Screens/FilePreviewScreen/InteractiveQuickLook.swift
@@ -153,11 +153,11 @@ private struct MediaPreviewViewController: UIViewControllerRepresentable {
 class MediaPreviewItem: NSObject, QLPreviewItem {
     let file: MediaFileHandleProxy
     
-    var previewItemURL: URL? {
+    nonisolated var previewItemURL: URL? { // nonisolated as QuickLook can call from any thread (macOS 26).
         file.url
     }
     
-    let previewItemTitle: String?
+    nonisolated let previewItemTitle: String? // nonisolated as QuickLook can call from any thread (macOS 26).
     
     init(file: MediaFileHandleProxy, title: String?) {
         self.file = file
diff --git a/ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewDataSource.swift b/ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewDataSource.swift
index 78b55b9bb..fbd0f75f3 100644
--- a/ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewDataSource.swift
+++ b/ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewDataSource.swift
@@ -9,6 +9,7 @@
 import Combine
 import Foundation
 import QuickLook
+import Synchronization
 
 /// A dedicated data source for QLPreviewController to support timeline updates. This was added to
 /// workaround the fact that calling `reloadData` on the controller **always** reloads the current
@@ -147,8 +148,14 @@ enum TimelineMediaPreviewItem: Equatable {
     
     /// Wraps a media file and title to be previewed with QuickLook.
     @Observable class Media: NSObject, QLPreviewItem, Identifiable {
-        fileprivate(set) var timelineItem: EventBasedMessageTimelineItemProtocol
-        var fileHandle: MediaFileHandleProxy?
+        fileprivate(set) var timelineItem: EventBasedMessageTimelineItemProtocol {
+            didSet { updatePreviewItemValues() }
+        }
+        
+        var fileHandle: MediaFileHandleProxy? {
+            didSet { updatePreviewItemValues() }
+        }
+        
         var downloadError: Error?
         
         init(timelineItem: EventBasedMessageTimelineItemProtocol) {
@@ -184,15 +191,22 @@ enum TimelineMediaPreviewItem: Equatable {
         
         // MARK: QLPreviewItem
         
-        var previewItemURL: URL? {
-            fileHandle?.url
+        private let _previewItemURL = Mutex<URL?>(nil)
+        nonisolated var previewItemURL: URL? { // nonisolated as QuickLook can call from any thread (macOS 26).
+            _previewItemURL.withLock { $0 }
         }
         
-        var previewItemTitle: String? {
-            switch fileHandle?.url {
-            case .some: filename
-            case .none: " " // Don't show any background text when the preview is still loading.
-            }
+        private let _previewItemTitle = Mutex<String?>(" ")
+        nonisolated var previewItemTitle: String? { // nonisolated as QuickLook can call from any thread (macOS 26).
+            _previewItemTitle.withLock { $0 }
+        }
+        
+        private func updatePreviewItemValues() {
+            let url = fileHandle?.url
+            _previewItemURL.withLock { $0 = url }
+            
+            // Don't show any background text (" ") while the preview is still loading.
+            _previewItemTitle.withLock { $0 = url == nil ? " " : filename }
         }
         
         // MARK: Event details
diff --git a/ElementX/Sources/Screens/LogViewerScreen/View/LogViewerScreen.swift b/ElementX/Sources/Screens/LogViewerScreen/View/LogViewerScreen.swift
index 476c67aaf..aaf26e467 100644
--- a/ElementX/Sources/Screens/LogViewerScreen/View/LogViewerScreen.swift
+++ b/ElementX/Sources/Screens/LogViewerScreen/View/LogViewerScreen.swift
@@ -63,8 +63,8 @@ private struct PreviewView: UIViewControllerRepresentable {
 }
 
 private class PreviewItem: NSObject, QLPreviewItem {
-    var previewItemURL: URL?
-    var previewItemTitle: String?
+    nonisolated let previewItemURL: URL? // nonisolated as QuickLook can call from any thread (macOS 26).
+    nonisolated let previewItemTitle: String? // nonisolated as QuickLook can call from any thread (macOS 26).
     
     init(previewItemURL: URL?, previewItemTitle: String?) {
         self.previewItemURL = previewItemURL
diff --git a/ElementX/Sources/Screens/MediaUploadPreviewScreen/View/MediaUploadPreviewScreen.swift b/ElementX/Sources/Screens/MediaUploadPreviewScreen/View/MediaUploadPreviewScreen.swift
index 25c1dfc56..3bb7f0e99 100644
--- a/ElementX/Sources/Screens/MediaUploadPreviewScreen/View/MediaUploadPreviewScreen.swift
+++ b/ElementX/Sources/Screens/MediaUploadPreviewScreen/View/MediaUploadPreviewScreen.swift
@@ -289,8 +289,8 @@ private struct PreviewView: UIViewControllerRepresentable {
 }
 
 private class PreviewItem: NSObject, QLPreviewItem {
-    var previewItemURL: URL?
-    var previewItemTitle: String?
+    nonisolated let previewItemURL: URL? // nonisolated as QuickLook can call from any thread (macOS 26).
+    nonisolated let previewItemTitle: String? // nonisolated as QuickLook can call from any thread (macOS 26).
     
     init(previewItemURL: URL?, previewItemTitle: String?) {
         self.previewItemURL = previewItemURL