How is portals configured on Cachy as it works correctly but not on other distros such as EndeavourOS?

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2

Check: Regression: D-Bus service does not start in MATE (1.21.1) · Issue #1983 · flatpak/xdg-desktop-portal · GitHub

After the latest update, xdg-desktop-portal requires graphical-session.target, which can be a problem in lightweight desktop environments and window managers.

Try:

systemctl --user start xdg-desktop-portal.service --ignore-dependencies