The display on the top left shows what signal is sent to the TV so let's hear what the source signal is.
As to the Youtube, yes, it's usually limited to lower resolutions. Again, it's no PC.
So I bought a brand new un75h7150 TV. Just hooked it up, but I am only seeing TV Channels in 720p, and not in 1080p? I Have two other tv's in the house, and they both display in 1080p. I tried changing the HDMI cable, but that did nothing, I also tried changing the cable box with one of the other tv's just to make sure that wasn't the problem and it wasn't. I tried all the HDMI connections on the back of the tv, and that did not fix the issue. When I turn the TV on it shows HDMI in the top left and 1280X720 60. On my other Samsung TV it shows as 1920X1080 60, as does our small Toshiba tv? I tried resetting the tv back to factory settings but that did nothing. I have also noted using You Tube, from a web browser, the highest resolution I could select is 720p. Am I missing something?
The Source is an Eastlink Cable box, that outputs 1080P, My other Samsung tv (un60es8000 with 2014 Evolution Kit) displays 1920X1080, as does the Toshiba when I connect them to the box and not 1280X720 as this one is displaying on the top left. I have used the same HDMI cable, and same cable box on all TV's as a test.
This one tip will help you sleep better tonight
A few seconds are all you need to get a better night's rest.