Access denied when initializing FileOpenPicker with HWND

Question

I was following https://stackoverflow.com/a/57599016/8800839 to register the window to the filepicker, because I ran into the same problem. While doing so, I get an "Access Denied" error while calling Initialize on IInitializeWithWindow

Output right before the window closes:

[src\main.rs:22] interop.WindowHandle() = Ok(
    HWND(
        12259034,
    ),
)
[src\main.rs:23] file_picker_i.Initialize(hwnd) = Err(
    Error {
        code: 0x80070005,
        message: Access is denied.
        ,
    },

main.rs:

#![allow(non_snake_case)]
use windows::core::*;
use windows::ApplicationModel::Activation::LaunchActivatedEventArgs;
use windows::ApplicationModel::Package;
use windows::Storage::Pickers::{FileOpenPicker, PickerLocationId, PickerViewMode};
use windows::UI::Xaml::*;
use windows::Win32::Foundation::HWND;
use windows::Win32::System::Com::{COINIT_MULTITHREADED, CoInitializeEx};
use windows::Win32::System::WinRT::ICoreWindowInterop;
use windows::Win32::UI::WindowsAndMessaging::{MB_ICONSTOP, MB_OK, MessageBoxW};
use windows::Win32::UI::Shell::IInitializeWithWindow;

#[implement(IApplicationOverrides)]
struct App ();
impl IApplicationOverrides_Impl for App {
    fn OnLaunched(&self, _: &Option<LaunchActivatedEventArgs>) -> Result<()> {
        let window = Window::Current()?;
        let interop = window.CoreWindow()?.cast::<ICoreWindowInterop>()?;
        let file_picker = FileOpenPicker::new()?;
        let file_picker_i = file_picker.cast::<IInitializeWithWindow>()?;
        unsafe {
            let hwnd = dbg!(interop.WindowHandle())?;
            dbg!(file_picker_i.Initialize(hwnd))
        }
    }
}
fn main() -> Result<()> {
    unsafe {
        CoInitializeEx(std::ptr::null(), COINIT_MULTITHREADED)?;
        if let Err(result) = Package::Current() {
            MessageBoxW(
                HWND::default(),
                "This sample must be registered (via register.cmd) and launched from Start.",
                "Error",
                MB_ICONSTOP | MB_OK,
            );
            return Err(result);
        }
    }
    Application::Start(ApplicationInitializationCallback::new(move |_| {
        Application::compose(App())?;
        Ok(())
    }))
}

Cargo.toml:

...
[dependencies.windows]
version = "0.35.0"
features = [
    "alloc",
    "implement",
    "ApplicationModel_Activation",
    "UI_Core",
    "UI_Xaml_Controls",
    "UI_Xaml",
    "Storage",
    "Storage_Pickers",
    "System",
    "Win32_System_WinRT",
    "Foundation_Collections",
    "UI_Xaml_Controls_Primitives",
    "Win32_Foundation",
    "Win32_Storage_Packaging_Appx",
    "Win32_System_Com",
    "Win32_UI_Shell",
    "Win32_UI_WindowsAndMessaging",
]
...

What is the cause of this error, and how can I overcome this error (to successfully use the FileOpenPicker)?