fractal flatpak fails to issue notifications
xdg-desktop-portal is dropping notifications from fractal because fractal uses Matrix users' avatars as the icon for the notification:
But user-provided avatars generally fail icon validation, as performed by /usr/libexec/flatpak-validate-icon.
fractal's notifications are being rejected by xdg-desktop-portal itself, so they are never passed on to xdg-desktop-portal-gtk.