Version 0.1.0 of package Filechooser has just been released in GNU ELPA. You can now find it in M-x list-packages RET.
Filechooser describes itself as: ================================= An xdg-desktop-portal filechooser ================================= More at https://elpa.gnu.org/packages/filechooser.html ## Summary: An implementation of xdg-desktop-portal filechooser in Emacs. This allows for choosing files in applications like firefox (with GTK_USE_PORTAL set) from an Emacs frame. The default is to use `read-file-name' for choosing ## Recent NEWS: [Not available 🙁]