If you switch back to the TV speakers and play the same A/V content does the UHD badge then show up? If not, then it’s probably just coincidental that the display has changed when you added the Sonos soundbar and enabled the CEC protocol.
In any event, you might be best to speak with Sony customer support. I think anyone would be quite surprised, if attaching any soundbar to the TV actually altered the TV display settings in some way.
Sonos certainly does not touch the video feed at all, they work off of ARC, which has nothing whatsoever to do with it.
Many thanks for prompt response. Definitely not getting the hdr content as previously. Removed the Sonos cable, and problem persists. However, I don’t think it’s a “coincidence”. Ie something in the hdmi/cec settings seems to have compromised the hdr. Am going to post a query on the Sony forum and will report back.
Kind regards.