Add kodi flatpak standalone as session entry to gdm (gnome)

Hello,
I’m trying to add a session entry for gdm to start kodi standalone.
When I was using the default kodi package it was already there but now I’m using the flatpak version and cannot get a kodi session listed.

I recreated /usr/share/xsessions/kodi.desktop and changed the exec line.

[Desktop Entry]
Name[de]=Kodi
Name[en_GB]=Kodi
Name=Kodi
Comment[de]=Diese Sitzung meldet Sie bei Kodi an
Comment[en_GB]=This session logs you into Kodi
Comment=This session logs you into Kodi
Exec=/usr/bin/flatpak run tv.kodi.Kodi --standalone --windowing=x11
Type=Application

But unfortunately gdm shows no kodi entry