diff --git a/Sources/SpeziViews/Views/Layout/HorizontalGeometryReader.swift b/Sources/SpeziViews/Views/Layout/HorizontalGeometryReader.swift
index c2a3011..bb618dd 100644
--- a/Sources/SpeziViews/Views/Layout/HorizontalGeometryReader.swift
+++ b/Sources/SpeziViews/Views/Layout/HorizontalGeometryReader.swift
@@ -39,7 +39,13 @@ public struct HorizontalGeometryReader<Content: View>: View {
                 }
             )
             .onPreferenceChange(WidthPreferenceKey.self) { width in
-                self.width = width
+                // The `onPreferenceChange` view modfier now takes a `@Sendable` closure, therefore we cannot capture `@MainActor` isolated properties
+                // on the `View` directly anymore: https://developer.apple.com/documentation/swiftui/view/onpreferencechange(_:perform:)?changes=latest_minor
+                // However, as the `@Sendable` closure is still run on the MainActor (at least in my testing on 18.2 RC SDKs), we can use `MainActor.assumeIsolated`
+                // to avoid scheduling a `MainActor` `Task`, which could delay execution and cause unexpected UI behavior.
+                MainActor.assumeIsolated {
+                    self.width = width
+                }
             }
     }
     
diff --git a/Tests/UITests/TestApp/ViewsTests/CanvasTestView.swift b/Tests/UITests/TestApp/ViewsTests/CanvasTestView.swift
index 9a9eafc..f56bd36 100644
--- a/Tests/UITests/TestApp/ViewsTests/CanvasTestView.swift
+++ b/Tests/UITests/TestApp/ViewsTests/CanvasTestView.swift
@@ -47,7 +47,10 @@ struct CanvasTestView: View {
             }
             .navigationBarTitleDisplayMode(.inline)
             .onPreferenceChange(CanvasView.CanvasSizePreferenceKey.self) { size in
-                self.receivedSize = size
+                // See `HorizontalGeometryReader.swift`
+                MainActor.assumeIsolated {
+                    self.receivedSize = size
+                }
             }
     }
 }
diff --git a/Tests/UITests/UITests.xcodeproj/project.pbxproj b/Tests/UITests/UITests.xcodeproj/project.pbxproj
index 0ec3d25..e0036d2 100644
--- a/Tests/UITests/UITests.xcodeproj/project.pbxproj
+++ b/Tests/UITests/UITests.xcodeproj/project.pbxproj
@@ -572,7 +572,7 @@
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_STRICT_CONCURRENCY = complete;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,3,7";
 			};
 			name = Debug;
@@ -606,7 +606,7 @@
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_STRICT_CONCURRENCY = complete;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,3,7";
 			};
 			name = Release;
@@ -629,7 +629,7 @@
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = NO;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				TEST_TARGET_NAME = TestApp;
 			};
@@ -652,7 +652,7 @@
 				SUPPORTS_MAC_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = NO;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				TEST_TARGET_NAME = TestApp;
 			};
@@ -753,7 +753,7 @@
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_STRICT_CONCURRENCY = complete;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,3,7";
 			};
 			name = Test;
@@ -776,7 +776,7 @@
 				SUPPORTS_XR_DESIGNED_FOR_IPHONE_IPAD = NO;
 				SWIFT_EMIT_LOC_STRINGS = NO;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				TEST_TARGET_NAME = TestApp;
 			};