Right okay that may explain it. It’s a 55” Sony OLED. I’ve another thread that mentioned the setup and shows images. I will be honest I paid £500 for it all. Would you recommend changing the NVR? Or are the cameras low end too?
Unless you're just viewing the cameras momentarily eg you hear a noise outside, flick from tv to the camera to check then back, I wouldn't recommend an OLED. You will experience screen burn with a static image and a camera interface has menus and other frames that are static. If the OLED is for dual useage as I described, then it's fine. If it's your intention to keep it permanently with CCTV on screen or switch between CCTV and TV but have it on CCTV for long periods, then I wouldn't recommend using it for that purpose. I got given a brand new OLED a few years ago (top brand) as a present and in just over 2.5 years, I had to send it back under warranty and swap it for an LED because watching Youtube on it had burn't the Youtube logos and play bars into the the screen even though I watched most videos fullscreen and without bars. The simple fact with OLED's is those phosphors only have a certain lifespan for each colour pigment. If you keep lighting the same area up in the same colour for extended periods or repeatedly, then overtime, that colour phosphor will start to weaken and you'll get a perment burn into the screen as that area will no longer be able to adequately produce whatever the dominent colour was in that area and thus other colours such as white, will not be able to display properly and you'll find a ghost logo burn into the screen as I did of the colour minus the deficient phosphor. eg in my case the logos were red, so I ended up with a greenish / blue ghosting. As I said above, this was the cumulative effect of watching Youtube, despite only having the play bar, logos etc onscreen for a short period of time whilst searching before going fullscreen was enough to permanently damage my tv. If you need a permanent diplay for CCTV, consider a 4k PC display or an LED tv. There's still a chance of retention with an LED tv over a long period of time, but it's lower than with OLED and may be fixable.
So far as you existing cameras go, nothing wrong with those cameras. There are better choices such as the 4Kx and 5442's Andy sells. However, as other mentioned the problem here is almost certainly your NVR which is feeding your display with very low resolution images, way below that of the cameras native resolution. Also note here, different TV's upscale better at different resolutions. eg on my current tv which is a very good one, 1080P > 4K is excellent. 720P > HD is aweful. Bear that in mind as your NVR may be feeding very low resolution video to your tv.