Did you also try Computer->UltraHD and see what you get?
Selecting Device->TV, might be that common broadcast formats are used which is much more limited and what is considered high quality is lower than media formats.
Hi Larioso yes I thought same as you so tried both Devices>TV and Devices>Computer, with the Ultra HD settings - no difference.
My 4K output habit is to Export&Share > Devices > Custom > Advanced (a button) > Match Source (another a button). It will save a preset that is very close to the original footage. When I tested it on a single clip, the output file size was about the same as the input file size. Compression seems non existent. I get confused on codecs, but it seems to use H.264 and does not mention use of XAVC-S.
I copy the output MP4 file on a USB flash/thumbdrive and plug that into my 4K TV. I don't use a Blu-Ray or any other media player. The Samsung TV sees and plays all the videos on my flash/thumb drive in glorious quality!
Brilliant - that done it thanks Bill!! All good now.
The stock export presets look to be a bit of a trap for young players if you are aiming for max quality!