As per the Windows App SDK release servicing policy, Windows App SDK releases prior to 1.7 are out of support, but there's still lots of 1.5 usage:
> findstr /spim /c:"Microsoft.WindowsAppSDK.1.5" *.vcxproj
DynamicDependenciesSample\DynamicDependencies\DirectX\D3D9ExSample.vcxproj
Samples\AppLifecycle\Activation\cpp\cpp-console-unpackaged\CppWinRtConsoleActivation\CppWinRtConsoleActivation.vcxproj
Samples\AppLifecycle\Activation\cpp\cpp-win32-packaged\CppWinMainActivation\CppWinMainActivation.vcxproj
Samples\AppLifecycle\Activation\cpp\cpp-win32-unpackaged\CppWinMainActivation\CppWinMainActivation.vcxproj
Samples\AppLifecycle\Activation\cpp\cpp-winui-packaged\CppWinUiDesktopActivation\CppWinUiDesktopActivation\CppWinUiDesktopActivation.vcxproj
Samples\AppLifecycle\EnvironmentVariables\cpp-console-unpackaged\CppWinRtConsoleEnv\CppWinRtConsoleEnv.vcxproj
Samples\AppLifecycle\EnvironmentVariables\cpp-win32-unpackaged\CppWinMainEnv\CppWinMainEnv.vcxproj
Samples\AppLifecycle\Instancing\cpp\cpp-console-unpackaged\CppWinRtConsoleInstancing\CppWinRtConsoleInstancing.vcxproj
Samples\AppLifecycle\Instancing\cpp\cpp-win32-packaged\CppWinMainInstancing\CppWinMainInstancing.vcxproj
Samples\AppLifecycle\Instancing\cpp\cpp-win32-unpackaged\CppWinMainInstancing\CppWinMainInstancing.vcxproj
Samples\AppLifecycle\Instancing\cpp\cpp-winui-packaged\CppWinUiDesktopInstancing\CppWinUiDesktopInstancing\CppWinUiDesktopInstancing.vcxproj
Samples\AppLifecycle\Restart\cpp-console-unpackaged\cpp-console-unpackaged.vcxproj
Samples\AppLifecycle\RestartRegistration\cpp-winui-packaged\cpp-winui-packaged.vcxproj
Samples\AppLifecycle\StateNotifications\cpp\cpp-console-unpackaged\CppWinRtConsoleState\CppWinRtConsoleState.vcxproj
Samples\AppLifecycle\StateNotifications\cpp\cpp-win32-packaged\CppWinMainState\CppWinMainState.vcxproj
Samples\AppLifecycle\StateNotifications\cpp\cpp-win32-unpackaged\CppWinMainState\CppWinMainState.vcxproj
Samples\AppLifecycle\StateNotifications\cpp\cpp-winui-packaged\CppWinUiDesktopState\CppWinUiDesktopState\CppWinUiDesktopState.vcxproj
Samples\Composition\DynamicRefreshRateTool\cpp-winui\DynamicRefreshRateTool.vcxproj
Samples\CustomControls\CppApp\CppApp.vcxproj
Samples\CustomControls\CppAppUnpackaged\CppAppUnpackaged.vcxproj
Samples\DeploymentManager\cpp-winui\DeploymentManagerSample.vcxproj
Samples\Insights\cpp-win32\InsightsSample.vcxproj
Samples\Mica\cpp-WebView2\Mica-WebView2\MicaWebView2.vcxproj
Samples\Mica\cpp-win32\WinAppSDKMicaSample\WinAppSDKMicaSample.vcxproj
Samples\Notifications\App\CppUnpackagedAppNotifications\CppUnpackagedAppNotifications\CppUnpackagedAppNotifications.vcxproj
Samples\Notifications\Push\cpp-console-packaged\cpp-console.vcxproj
Samples\Notifications\Push\cpp-console-unpackaged\cpp-console-unpackaged.vcxproj
Samples\PhotoEditor\cpp-winui\PhotoEditor\PhotoEditor.vcxproj
Samples\ResourceManagement\cpp\cpp-console-unpackaged\console_unpackaged_app.vcxproj
Samples\ResourceManagement\cpp\cpp-winui\winui_desktop_packaged_app_cpp\winui_desktop_packaged_app_cpp.vcxproj
Samples\SelfContainedDeployment\cpp\cpp-console-unpackaged\SelfContainedDeployment.vcxproj
Samples\SelfContainedDeployment\cpp\cpp-winui-packaged\SelfContainedDeployment.vcxproj
Samples\SelfContainedDeployment\cpp\cpp-winui-unpackaged\SelfContainedDeployment.vcxproj
Samples\TextRendering\cpp-win32\DWriteCoreGallery\DWriteCoreGallery.vcxproj
Samples\Unpackaged\cpp-console-unpackaged\Unpackaged.vcxproj
Samples\Widgets\cpp-win32-packaged\SampleWidgetProviderApp\SampleWidgetProviderApp.vcxproj
Samples\Windowing\cpp\cpp-winui\SampleApp\SampleApp.vcxproj
As per the Windows App SDK release servicing policy, Windows App SDK releases prior to 1.7 are out of support, but there's still lots of 1.5 usage: