Thanks you for that, JerryLBell.
Anyone have other suggetions for content that show off 4K and HDR?
My computer can be connected to 4K HDR TV via HDMI.
So need not be a 4K bluray disc player.
Even a "spectaclular demontration" sample file would be good to show off why a 4K HDR TV is perceivably better.
Anyone here, have a URL or a recommendation for some content?

Thanks.

My 75 inch Sony TV has a sample 4K video built in to the TV. I don't know if other brands have the same feature. If you have Xfinity cable TV, they have a 4K cable box that you can upgrade to. And, YouTube has a lot of free 4K videos. Just do a "4K video" search.

Nature shows like Planet Earth II are a great thing for showing off a good TV. The main streaming sources (NetFlix, Google Prime, Disney+) all have several in 4K. The video is compressed to a lower bitrate than on 4K discs so they won't be quite as good as on a 4K disc (also called a UHD disc). Of course, a standard Blu-ray disc player won't be able to play these discs; you'lll need to upgrade to a 4K/UHD-compatible Blu-ray player. And if you want to play discs that have HDR encoded (whether HDR10 or Dolby Vision), you'll need to select a player that supports that as well.

Note that Blu-ray players that come with computers don't necessarily have the ability to play the triple- or quadruple-layer Blu-ray discs that 4K movies come on. They mostly have the ability to play single- or double-layer Blu-ray discs that HD movies come on.

Here's a site that has sample 4K files (most in MKV format, some in MP4 format), some with HDR but most without. Many of these are the demo files that are shown in a loop on TVs at electronics stores. 4K Media | Free Ultra-HD / HDR / HLG / Dolby Vision 4K Video Demos & Samples

On my Roku TV, a Dolby streaming site app came pre-installed that has a few spectacular (though very short) demo files as well. Shop through your app store for that or just on "4K" or "UHD" in general.

I still have my 50" Panasonic Vierra plasma TV even though it is broken. I need to get it to a vendor to repair the power supply on it. When these were released, seemingly every electronics website on the web was tripping over its own feet praising it as the best TV you could buy at any price.

So if it's broken, why keep it? Well, it may not do 4K but it does do HD very, very well and it does 3D HD. I can't find any 4K TVs that support 3D. I'm not a huge fan of 3D as most of the 60 or so films I have in 3D really aren't that great but the few that are (Avatar, Gravity and David Attenboro's Kingdom of Plants 3D come to mind) really, really look good in 3D.

Had one of those too on Maui. It only lasted 5 years due to salt air corrosion (typical for electronics in Hawai'i). Weighed around 150 lbs as I recall. Great pic though.