System.Exception: XOpenDisplay failed on Fedora KDE Spin

Hi,

I have been using without much trouble the Flatpak Stable version of RDM on Fedora 41 KDE Spin.
Today RDM no longer runs, unfortunately, and when I try to manually run it from a terminal I get this error:

username@hostname ~> /usr/bin/flatpak run --branch=stable --arch=x86_64 --command=remotedesktopmanager --file-forwarding net.devolutions.RDM @@u %U @@
Unhandled exception. System.Exception: XOpenDisplay failed
   at Avalonia.X11.AvaloniaX11Platform.Initialize(X11PlatformOptions options)
   at Avalonia.AppBuilder.SetupUnsafe()
   at Avalonia.AppBuilder.SetupWithoutStarting()
   at Devolutions.RemoteDesktopManager.Program.Main(String[] args)

Is there any additional argument that would tell RDM to which display to connect?
Thank you.