It’s almost certainly a xdg-dektop-portal bug that is affecting other DEs. See this topic on the Arch Linux forum that includes a solution that works for me on Xfce - https://bbs.archlinux.org/viewtopic.php?pid=2300839#p2300839
Stop xdg-desktop-portal.service first with:
systemctl --user stop xdg-desktop-portal.service
Create an empty file called “xdg-desktop-portal.service” in /home/yourusername/.config/systemd/user (you might need to create the systemd and user folders)
In this file add this text from the Arch forum post I linked to above 
[Unit]
Description=Portal service
PartOf=graphical-session.target
#Requisite=graphical-session.target # removed = workaround
Requires=dbus.service
After=dbus.service graphical-session-pre.target
[Service]
Type=dbus
BusName=org.freedesktop.portal.Desktop
ExecStart=/usr/lib/xdg-desktop-portal
Slice=session.slice
Save and exit the file, then restart xdg-desktop-portal.service with:
systemctl --user start xdg-desktop-portal.service
Try running this again and check the output:
systemctl --user status xdg-desktop-portal.service