Open the file manager from a flatpak application

Hello, I have created a flatpak to my downloader app.

How can I open the file manager from my application? It appears that calling xdg-open file:///path/to/folder does not seem to work. The file manager is not launched. The app has been given access to that of - --filesystem=host permission.

I tested xdg-open $HOME and it didn’t work either.