A year ago I bought myself an LG 55" 4K HDR TV.
It's never been connected to an aerial or any kind of cable or satelite connection. It has only served as a media centre using a PC. For a while I used it's "apps" for Amazon Prime, Netflix, but I stopped and disconnected it from the network when it did this...
I hit the "Home" button on the TV and along the bottom it said, "Recently uploaded photos" and displayed a series of images I had no idea I had and... well... didn't really want them displayed on my TV dashboard if friends or family were round. It turns out it scanned my network and invited itself into some folders I had shared with DLNA. Buried in one of them was a folder of images I hadn't seen in years, but unfortunately a few dubious photos were present. With the TV applying a new update which contained a horrifying Privacy and data sharing policy, I unplugged the network cable and made sure it's Wifi was unconfigured.
Anyway... I was using a Dell Small Form Factor PC I found on EBay, it's a reconditioned 2nd gen i5 with 8Gb of RAM and a 512Gb SSD (for £120!). However the build in, Intel HD Graphics adapter maxed out at 1080p. "Oh noes!"
It wasn't until I happened across a YouTube video on turning one of this highly available corporate surplus PCs into a gaming machine that I realised you could actually fit a GPU in them.
Scored myself a brand new GTX 1030 for £60 on scamazon, it fitted perfectly, rebooted, installed the NVidia drivers and BOOM, full 4k display.
Amazon Prime works with it, YouTube works will it. I think Netflix want extra money for 4k, but I'm happy enough.
I tried a few of the remastered movies claiming to be 4K, but to be honest I don't think you really notice the difference. However a HQ YouTube stream from a big channel like Linus Tech Tips or similar is absolutely glorious looking. I think the remastered movies are a scam, they may be redigitized at 4k, but they are then absolutely annihilated by over compression removing any positive quality improvements. Maybe they are better on BlueRay or maybe it's just Amazon Prime that is over compressing.
As a bonus, I can now play games on the living room TV too. Sure it's pretty low end, but will do most games at low settings 1080p at 30FPS.