Today’s release of Plex for Mac and Windows 1.33 fixes the HD filter issue in the desktop clients, however, I see that Channel 236 - GBNews is listed as a HD channel:
… and that Gracenote call it GB News HD in the EPG data and tag it as HD:
I note that Freeview does not list it as a HD channel on the What HD channels can I watch on Freeview? page and that the Channel Listings page shows it on the ARQ B mux which I don’t believe is HD - has Gracenote incorrectly categorised it like they did with the Smithsonian Channel?
If I bring up the Video Settings in the Plex for Tizen client, it shows 480i (MPEG2VIDEO) and if I display on screen Information the codec is shown as mpeg2video → h264 and resolution as 544 x 576 → 1024 x 576.