I have two EOS installed. I installed the former on an external SSD (256GB; 38GB ext4 partition, of which 15 used) and the latter on my laptop’s SSD (256GB; 120GB ext4 partition, of which 21 used). The former is connected to the laptop via a USB-c to USB-A 3.0 converter. When I launch some applications using the EOS installed on my laptop (not all! Especially Firefox or Floorp, Thunderbird and Libreoffice), it takes 25 seconds to open the launched program!! When I do the same thing on the external drive, it takes 3 or 4 seconds. Normally it should be the other way around: the OS on the internal drive is faster, albeit without major differences. I specify that it cannot be a hardware problem because the two SSDs are similar in performance and before installing EOS on the internal SSD I tested another (Arch)Linux distro (BlendOS) installed on the same partition, which worked quickly. One last information: all the packages installed in the two systems are Archlinux/EOS packages, not Flatpak and similar.
The only noticeable difference between the two installed EOS is in their desktops: the first (on the external drive) is the Archlinux XFCE4 version that I installed directly via pacman and the second (on the portable drive) is the EOS XFCE4 version contained in the EOS ISO. The former is more basic, the latter more elaborate, but I don’t think it’s sufficient to explain such a difference in performance.
I would like to keep the EOS XFCE4 version for its looks and feel but without that flaw.
If you have both installed, it will still choose xdg-desktop-portal-gnome since it is higher in the list in alphabetical order. Therefore, the best option is to have it removed.
xdg-desktop-portal will use the XDG_CURRENT_DESKTOPenvironment variable to determine which backend it will use for the request. If more than one backend can be used for the current desktop, the first one in alphabetical order is chosen.