I tried that (a flatpak that wanted around a GB of additional flatpaks...) and I also get a back window. The krdp server says that when I connect:
org.kde.krdp: Video stream initialized
org.kde.krdp: Received caps:
org.kde.krdp: RDPGFX_CAPVERSION_8 AVC: false YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_81 AVC: true YUV420: true
org.kde.krdp: RDPGFX_CAPVERSION_10 AVC: true YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_101 AVC: true YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_102 AVC: true YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_103 AVC: true YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_104 AVC: true YUV420: true
org.kde.krdp: RDPGFX_CAPVERSION_105 AVC: true YUV420: true
org.kde.krdp: RDPGFX_CAPVERSION_106 AVC: true YUV420: true
org.kde.krdp: UNKNOWN_VERSION AVC: false YUV420: false
org.kde.krdp: RDPGFX_CAPVERSION_107 AVC: true YUV420: true
org.kde.krdp: Selected caps: RDPGFX_CAPVERSION_107
I guess this is not for this list.
--
Roger Oberholtzer